A controlled process for precipitating polymorphs of calcium carbonate

ABSTRACT

A process for converting gypsum into precipitated calcium carbonate including reacting a mixture comprising gypsum and a seed, a mineral acid, or both with at least one carbonate source, whereby precipitated calcium carbonate is produced in the form of calcite and/or aragonite directly without conversion from a vaterite polymorph. Also, a process for converting gypsum into precipitated calcium carbonate including providing a mixture comprising i) gypsum ii) a seed, a mineral acid, or both iii) at least one additive selected from the group consisting of ammonium sulfate, an organic acid, or an iron material, and reacting the mixture with at least one carbonate source to produce precipitated calcium carbonate in the form of vaterite. The precipitated calcium carbonates having desired and unique composition, polymorph and crystal size characteristics formed by these processes.

CLAIM FOR PRIORITY

This PCT International Application claims the benefit of priority ofU.S. Provisional Patent Application Nos. 62/103,425, filed Jan. 14,2015, 62/127,687, filed Mar. 3, 2015, 62/132,385, filed Mar. 12, 2015,and 62/206,594, filed Aug. 18, 2015, the subject matter of all of whichis incorporated herein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE Technical Field

The present disclosure relates to a controlled process for convertinggypsum into a precipitated calcium carbonate having desired polymorphand crystal size characteristics as well as precipitated calciumcarbonate compositions formed by the controlled process.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentdisclosure.

A power plant is an industrial facility for the generation of electricpower. Each power station contains one or more generators, a rotatingmachine that converts mechanical power into electrical power by creatingrelative motion between a magnetic field and a conductor. The energysource harnessed to turn the generator varies widely. Most powerstations in the world burn fossil fuels such as coal, oil, and naturalgas to generate electricity. Fossil fuel power plants are commonlycoal-fired power stations. These coal powered plants produce heat byburning coal in a steam boiler. The steam drives a steam turbine andgenerator that then produces electricity. A biomass-fueled power plantmay be fueled by waste from sugar cane, municipal solid waste, landfillmethane, or other forms of biomass. The waste products from theseprocesses include ash, sulfur dioxide, nitrogen oxides and carbondioxide. Some of the gases can be removed from the waste stream toreduce pollution.

Flue gas is the gas exiting to the atmosphere via a flue, which is apipe or channel for conveying exhaust gases from a fireplace, oven,furnace, boiler or steam generator. Quite often, the flue gas refers tothe combustion exhaust gas produced at power plants. The removal ofwaste products from flue gas, such as SO₂, is mandated by air qualityregulatory agencies to reduce the acid rain caused by coal burning. Toreduce the emissions of SO₂ from coal fired power plants thepost-combustion flue gas is treated with limestone that sequesters theSO₂ in the form of gypsum (e.g. calcium sulfate).

Coal plants that use flue gas desulfurization (herein referred to as“FGD”) to reduce sulfur content set very high specifications for thecalcium content of the limestone they use. There is a large market forcalcium sulfate from FGD for reuse in construction (e.g. Dry Wall),additionally as a solid with limited water solubility it can beeffectively isolated from the process water and landfilled as a solid ifrequired or converted into calcium carbonate by known processes.

Gypsum resulting from the FGD of coal fired power plants is an impureform of calcium sulfate. These impurities may have a major impact on thequality and polymorph of precipitated calcium carbonate obtained whenthe gypsum is reacted with carbonates. Magnesium sulfate, for example,is a co-product with the gypsum from the FGD process and is problematicas its high water solubility increases the difficulty of cleaning up theFGD process water. Overcoming these effects would be advantageous inproviding a consistent industrial calcium carbonate.

Producing precipitated calcium carbonate (PCC) by use of calcinednatural calcium carbonate is well-known and widely used in the industry.Calcining forces formation of calcium oxide from which a precipitatedcalcium carbonate is produced upon consecutive exposure to water andcarbon dioxide. The energy consumed in calcining natural calciumcarbonate is a large part of the production cost of precipitated calciumcarbonate.

In view of the foregoing, one aspect of the present disclosure relatesto precipitated calcium carbonate compositions with desired polymorphand crystal size and a controlled process for converting gypsum intosaid precipitated calcium carbonate while avoiding the aforementioneddisadvantages.

In other industries, such as drilling wells for hydrocarbon extraction,fluids may be used for a variety of reasons, such as lubrication andcooling of drill bit cutting surfaces while drilling, controllingformation fluid pressure to prevent blowouts, maintaining wellstability, suspending solids in the well, minimizing fluid loss into andstabilizing the formation through which the well is being drilled,fracturing the formation in the vicinity of the well, displacing thefluid within the well with another fluid, cleaning the well, testing thewell, emplacing a packer, abandoning the well or preparing the well forabandonment, and otherwise treating the well or the formation. Thesefluids should be capable of suspending additive weighting agents (toincrease specific gravity of the mud), generally finely ground barites(barium sulfate ore), and transport clay and other substances capable ofadhering to and coating the borehole surface. Conventional weightingagents, however, may have undesirable properties. For example, theweighting agents, such as iron oxide-based weighting agents may beoverly abrasive and can cause damage or corrosion to well equipment.Similarly, barium sulfate agents may fill cracks in the well formation,thereby inhibiting flow of the hydrocarbon to be extracted. It may bedesirable, therefore, to provide improved additives, such as weightingagents, with improved properties.

SUMMARY

According to a first aspect, the present disclosure relates to aprecipitated calcium carbonate having a calcite polymorph that meets atleast one of the following: a stearic acid uptake surface area rangingfrom 1 to 30 m²/g, or at least one impurity by weight relative to thetotal weight of the precipitated calcium carbonate selected from thegroup consisting of: (i) Fe greater than 0.04 wt %, (ii) NH₄OH rangingfrom 0 to 35 wt %, (iii) (NH₄)₂CO₃ ranging from 0 to 40 wt %, (iv)(NH₄)₂SO₄ ranging from 0 to 35 wt %, (v) CaSO₄ ranging from 10 to 50 wt%, (vi) MgCO₃ ranging from 2 to 50 wt %, and (vii) CaO ranging from 5 to10 wt %.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a BET surface area ranging from 1-30 m²/g.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a d₅₀ particle size ranging from 1 to 28 μm.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a d₉₀ particle size ranging from 2 to 25 μm.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a d₁₀ particle size ranging from 0.1 to 4 μm.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a steepness (100×d₃₀/d₇₀) ranging from 30 to 100.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has an ISO brightness ranging from 54-96.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a DIN yellow index ranging from 0.7 to 10.3.

According to a second aspect, the present disclosure relates to aprecipitated calcium carbonate having a calcite polymorph, which emitsan amount of carbon dioxide during production that is less than anamount of carbon dioxide emitted during the production of a precipitatedcalcium carbonate having a calcite polymorph produced by calcining andslaking natural calcium carbonate.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a BET surface area ranging from 1-30 m²/g.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a stearic acid uptake surface area ranging from 1-30m²/g.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a d₅₀ particle size ranging from 1 to 28 μm.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a d₉₀ particle size ranging from 2 to 25 μm.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a d₁₀ particle size ranging from 0.1 to 4 μm.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a steepness (100×d₃₀/d₇₀) ranging from 30 to 100.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has an ISO brightness ranging from 54-96.

In one embodiment, the precipitated calcium carbonate having a calcitepolymorph also has a DIN yellow index ranging from 0.7 to 10.3.

According to a third aspect, the present disclosure relates to aprecipitated calcium carbonate having a low carbon footprint comprisinga calcite calcium carbonate polymorph and a first amount of Fe, whereinthe first amount of Fe is inversely correlated to carbon dioxideemissions, and wherein the first amount of Fe is greater than a secondamount of Fe present in a precipitated calcium carbonate produced bycalcining and slaking natural calcium carbonate.

In one embodiment, the first amount of Fe is greater than 0.04 wt %relative to the total weight of the precipitated calcium carbonatehaving a low carbon footprint.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a BET surface area ranging from 1-30 m²/g.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a stearic acid uptake surface area ranging from1-30 m²/g.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a d₅₀ particle size ranging from 1 to 28 μm.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a d₉₀ particle size ranging from 2 to 25 μm.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a d₁₀ particle size ranging from 0.1 to 4 μm.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a steepness (100×d₃₀/d₇₀) ranging from 30 to 100.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has an ISO brightness ranging from 54-96.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a DIN yellow index ranging from 0.7 to 10.3.

According to a fourth aspect, the present disclosure relates to a paperproduct, comprising a precipitated calcium carbonate having a calcitepolymorph, in one or more of its embodiments, wherein the precipitatedcalcium carbonate is present in the paper product as a filler or as acoating.

In one embodiment, the paper product is a paper towel, and absorbentcloth, or a sanitary napkin.

According to a fifth aspect, the present disclosure relates to a polymercomprising a polymeric material and a filler, wherein the fillercomprises a precipitated calcium carbonate having a calcite polymorph,in one or more of its embodiments.

According to a sixth aspect, the present disclosure relates to aprecipitated calcium carbonate having an aragonite polymorph that meetsat least one of the following: a stearic acid uptake surface arearanging from 2 to 30 m²/g, or at least one impurity by weight relativeto the total weight of the precipitated calcium carbonate selected fromthe group consisting of: (i) Fe greater than 0.04 wt %, (ii) NH₄OHranging from 0 to 35 wt %, (iii) (NH₄)₂CO₃ ranging from 0 to 40 wt %,(iv) (NH₄)₂SO₄ ranging from 0 to 35 wt %, (v) CaSO₄ ranging from 10 to50 wt %, (vi) MgCO₃ ranging from 2 to 50 wt %, and (vii) CaO rangingfrom 5 to 10 wt %.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a BET surface area ranging from 2-30 m²/g.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a d₅₀ particle size ranging from 0.1 to 10μm.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a d₉₀ particle size ranging from 2 to 25μm.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a d₁₀ particle size ranging from 0.05 to 4μm.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a steepness (100×d₃₀/d₇₀) ranging from 30to 100.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has an ISO brightness ranging from 54-99.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a DIN yellow index ranging from 0.7 to10.3.

According to a seventh aspect, the present disclosure relates to aprecipitated calcium carbonate having an aragonite polymorph, whichemits an amount of carbon dioxide during production that is less than anamount of carbon dioxide emitted during the production of a precipitatedcalcium carbonate having an aragonite polymorph produced by calciningand slaking natural calcium carbonate.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a BET surface area ranging from 2-30 m²/g.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a stearic acid uptake surface area rangingfrom 2-30 m²/g.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a d₅₀ particle size ranging from 0.1 to 10μm.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a d₉₀ particle size ranging from 2 to 25μm.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a d₁₀ particle size ranging from 0.05 to 4μm.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a steepness (100×d₃₀/d₇₀) ranging from 30to 100.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has an ISO brightness ranging from 54-99.

In one embodiment, the precipitated calcium carbonate having anaragonite polymorph also has a DIN yellow index ranging from 0.7 to10.3.

According to an eighth aspect, the present disclosure relates to aprecipitated calcium carbonate having a low carbon footprint comprisingan aragonite calcium carbonate polymorph and a first amount of Fe,wherein the first amount of Fe is inversely correlated to carbon dioxideemissions, and wherein the first amount of Fe is greater than a secondamount of Fe present in a precipitated calcium carbonate produced bycalcining and slaking natural calcium carbonate.

In one embodiment, the first amount of Fe is greater than 0.04 wt %relative to the total weight of the precipitated calcium carbonatehaving a low carbon footprint.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a BET surface area ranging from 2-30 m²/g.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a stearic acid uptake surface area ranging from2-30 m²/g.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a d₅₀ particle size ranging from 0.1 to 10 μm.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a d₉₀ particle size ranging from 2 to 25 μm.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a d₁₀ particle size ranging from 0.05 to 4 μm.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a steepness (100×d₃₀/d₇₀) ranging from 30 to 100.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has an ISO brightness ranging from 54-99.

In one embodiment, the precipitated calcium carbonate having a lowcarbon footprint has a DIN yellow index ranging from 0.7 to 10.3.

According to a ninth aspect, the present disclosure relates to a paperproduct, comprising a precipitated calcium carbonate having an aragonitepolymorph, in one or more of its embodiments, wherein the precipitatedcalcium carbonate is present in the paper product as a filler or as acoating.

In one embodiment, the paper product is a paper towel, and absorbentcloth, or a sanitary napkin.

According to a tenth aspect, the present disclosure relates to a polymercomprising a polymeric material and a filler, wherein the fillercomprises a precipitated calcium carbonate having an aragonitepolymorph, in one or more of its embodiments.

In one embodiment, the polymer is biodegradable.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an illustration of a flue gas desulfurizing apparatus.

FIG. 2 is an SEM image of a rhombic calcite, 300-500 nm.

FIG. 3 is an SEM image of a calcite and vaterite blend.

FIG. 4 is an SEM image of a rhombic calcite, ˜5 μm.

FIG. 5 is an SEM image of a vaterite and aragonite blend.

FIG. 6 is an SEM image of vaterite.

FIG. 7 is an SEM image of a vaterite and calcite blend produced fromgypsum and sodium carbonate.

FIG. 8 is an SEM image of a rhombic calcite, 300-500 nm fromcalcite-seeded gypsum.

FIG. 9 is an SEM image of a rhombic calcite, 1-3 μm from dolomiteseeded-gypsum.

FIG. 10 is an SEM image of a rhombic calcite, 5 μm from calciteseeded-gypsum.

FIG. 11 is an SEM image of a rhombic calcite, 300 nm-1 μm frommagnesite-seeded gypsum.

FIG. 12 is an SEM image of a calcite ˜300-500 nm with 2% calcite seedingand low theoretical ammonium bicarbonate content in ammonium carbonate.

FIG. 13 is an SEM image of a vaterite ˜300-500 nm with no seeding andlow theoretical ammonium bicarbonate content in ammonium carbonate.

FIG. 14 is an SEM image of a calcite ˜300-500 nm with 2% calcite seedingand high theoretical ammonium bicarbonate content in ammonium carbonate.

FIG. 15 is an SEM image of a Rhombic PCC from Crystal Seeding withcalcite seed.

FIG. 16 is an SEM image of a Rhombic PCC from Crystal Seeding withmagnesite seed.

FIG. 17 is an SEM image of a Rhombic PCC from Crystal Seeding withdolomite seed.

FIG. 18 is an SEM image of a Non-Rhombic Polymorph from Partial-CrystalSeeding of vaterite+aragonite from [calcite+MgCO₃ (1:3 molar ratio)]seeding.

FIG. 19 is an SEM image of a Non-Rhombic Polymorph from Non-CrystalSeeding of vaterite+aragonite from MgCO₃ seeding.

FIG. 20 is an SEM image of a Non-Rhombic Polymorph from Non-CrystalSeeding of vaterite rhombic calcite and aragonite from dolomiticquicklime seeding.

FIG. 21 is an SEM image of a Calcite, Vaterite from FGD Gypsum+AmmoniumCarbonate.

FIG. 22 is an SEM image of a Jamaican ore Seed GCC.

FIG. 23 is an SEM image of a Rhombic Calcite from Calcite-Seeded Gypsum.

FIG. 24 is an SEM image of a bluegrass ore Dolomite Seed GCC.

FIG. 25 is an SEM image of a Rhombic Calcite from Dolomite-SeededGypsum.

FIG. 26 is an SEM image of a Vaterite from Pure Gypsum (No Seeding) atLow Temp (12C).

FIG. 27 is an SEM image of a Calcite, Vaterite Blend from Pure Gypsum(No Seeding).

FIG. 28 is an SEM image of a Rhombic Calcite from Calcite-Seeded Gypsum.

FIG. 29 is an SEM image of a Large Rhombic Calcite from Calcite-SeededGypsum Reacted with Ammonium Carbonate Heated >46 C.

FIG. 30 is an SEM image of a Vaterite, Aragonite from Gypsum seeded withMgCO₃.

FIG. 31 is an SEM image of MgCO₃ from MgSO₄+Ammonium Carbonate.

FIG. 32 is an SEM image of MgCO₃ from MgSO₄+Ammonium Carbonate.

FIG. 33 is an SEM image of a Carbonate Blend (est. ˜7.3% MgCO₃, 22.4%MgCa(CO₃)₂ and 61.8% CaCO₃) from 1:1 [CaSO₄:MgSO₄]+Ammonium Carbonate.

FIG. 34 is an SEM image of MgCO₃ from MgSO₄+Sodium Carbonate.

FIG. 35 is an SEM image of a Vaterite, Calcite from Gypsum+SodiumCarbonate.

FIG. 36 is an SEM image of Gypsum, 99% (Sigma Gypsum) Used for MostTrials (Except Where Noted).

FIG. 37 is an SEM image of a US Gypsum.

FIG. 38 is an SEM image of a US Gypsum.

FIG. 39 shows SEM images of vaterite to calcite conversion for variousfeed concentrations and aging processes.

FIG. 40 shows SEM images for different feed concentrations.

FIG. 41 shows an SEM image and an exemplary measurement of squareness.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present disclosure will now be described more fullyhereinafter.

A Process for Desulfurizing Flue Gas to Form Gypsum

The present disclosure relates to a process for desulfurizing a flue gascomprising i) scrubbing a flue gas comprising sulfur dioxide with a SO₂sequestrating agent to yield a suspension comprising flue gasdesulfurized gypsum and an aqueous solution comprising magnesium sulfateii) separating the flue gas desulfurized gypsum from the magnesiumsulfate solution iii) reacting at least one carbonate salt with themagnesium sulfate solution to yield magnesium carbonate, which may be ofthe form magnesite and iv) isolating the magnesium carbonate ormagnesite.

In each of the particular embodiments herein, it is envisioned that theflue gas for desulfurization is obtained from a coal power plant, an oilpower plant, a natural gas power plant, and/or a biomass fueled plant.

Calcium carbonate used in the flue gas desulfurization process can bepure calcium carbonate or have added components, such as magnesium.Depending on the calcium and magnesium levels, calcium carbonate may beclassified as calcite or dolomite, among others.

Dolomite is an anhydrous carbonate mineral composed of calcium magnesiumcarbonate, e.g. CaMg(CO₃)₂. The word dolomite is also used to describethe sedimentary carbonate rock, which is composed predominantly of themineral dolomite. The mineral dolomite crystallizes in thetrigonal-rhombohedral system. It forms white, tan, gray, or pinkcrystals. Dolomite is a double carbonate, having an alternatingstructural arrangement of calcium and magnesium ions.

In terms of the present disclosure, magnesite may refer to thecrystalline form or the amorphous form of magnesium carbonate, MgCO₃.

In some embodiments, the SO₂ sequestrating agent can be, but is notlimited to, calcium-containing carbonate minerals including dolomite,calcite, vaterite, aragonite, ankerite, huntite, minrecordite,barytocite, ikaite, amorphous calcium carbonate, hydrates thereof, orcombinations thereof. In a certain embodiment, the SO₂ sequestratingagent is dolomite, or a hydrate thereof. In one embodiment, the SO₂sequestrating agent is vaterite of high surface area.

After scrubbing with dolomite or dolomitic limestone, the magnesiumsulfate rich supernatant of a spent carbonate stream is separated fromthe solid gypsum co-product by any conventional means, such asfiltration or centrifugation, and optionally recrystallizing the solidgypsum to obtain a product with a higher purity. Filtration methods maybe, but are not limited to, vacuum filtration. The purity of isolateddesulfurized gypsum may be variable, depending on the starting purity ofthe sulfur-containing flue gas.

According to some embodiments, a magnesium sulfate solution from theextraction of dolomite may be seeded with gypsum and/or a carbonate(such as calcium carbonate) to control the dolomite composition. Forexample, increasing the relative amount of gypsum may decrease dolomiteprecipitation, whereas relatively more ammonium carbonate may increasedolomite precipitation.

The supernatant is then treated with an appropriate carbonate salt toyield a value added precipitated magnesium carbonate, such as magnesite.In one embodiment, the carbonate salt comprises a carbonate orbicarbonate anion and at least one cation selected from the groupconsisting of sodium, calcium, cobalt, copper, potassium, ammonium,chromium, iron, aluminum, tin, lead, magnesium, silver, titanium,vanadium, zinc, lithium, nickel, barium, strontium, and hydronium. Theadded carbonate salt may be in solid form, in aqueous solution, or asuspension or slurry. Under conditions which the carbonate salt is addedas a solution or suspension, the pH of the solution or suspension may beacidic (pH less than 6.5), neutral (pH 6.5-7.5), or basic (pH greaterthan 7.5).

Magnesite is a mineral with the chemical formula MgCO₃ (magnesiumcarbonate). Naturally occurring magnesite generally is atrigonal-hexagonal scalenohedral crystal system. Similar to theproduction of lime, magnesite can be burned in the presence of charcoalto produce MgO, which in the form of a mineral is known as periclase.Large quantities of magnesite are burnt to make magnesium oxide, whichis a refractory material used as a lining in blast furnaces, kilns andincinerators. Magnesite can also be used as a binder in flooringmaterial. Furthermore it is being used as a catalyst and filler in theproduction of synthetic rubber and in the preparation of magnesiumchemicals and fertilizers. The isolated magnesite from the presentdisclosure, in particular, has value as a filler pigment especially forapplications which require some degree of acid resistance (foodpackaging, synthetic marble). In one embodiment, the isolated magnesitemay be amorphous with a surface area greater than 20 m²/g.

In one embodiment, the flue gas desulfurized gypsum is separated fromthe magnesium sulfate solution by filtration or centrifugation.

In the present disclosure, the gypsum isolated by filtration orcentrifugation can optionally be 1) used in the manufacture of wallboard or other construction materials, 2) landfilled, or 3) convertedinto calcium carbonate by known processes in the prior art or byprocesses disclosed hereinafter.

As to the gypsum for use in the present disclosure, there is noparticular limitation and the gypsum may be natural gypsum, synthetic(e.g., chemically produced) gypsum, FGD gypsum, and/or phosphogypsum.However, FGD gypsum and chemically produced gypsum are mentioned asexamples.

According to some embodiments, the FGD gypsum may be ground or milled.The grinding or milling of the FGD gypsum may be followed by one or moreof magnetic separation, bleaching, acid washing, or other beneficiationprocesses.

Pure gypsum is a soft sulfate mineral composed of calcium sulfatedihydrate, with the chemical formula CaSO₄.2H₂O. It can be used as afertilizer, is the main constituent in many forms of plaster and iswidely mined. Gypsum resulting from the flue gas desulfurization (FGD)of coal fired power plants is an impure form of calcium sulfate. Whenconverted into calcium carbonate, these impurities may have a majorimpact on the quality and polymorph of precipitated calcium carbonateobtained when the gypsum is reacted with ammonium sulfate. Magnesiumsulfate, for example, is a co-product with the gypsum from the FGDprocess and is problematic as its high water solubility increases thedifficulty of cleaning up the FGD process water. In this disclosure, USgypsum refers to impure gypsum, which generally is 80-90% pure. Thisgypsum typically contains impurities such as calcite and MgCO₃ and theseimpurities may be in about a 1:3 ratio. Raw gypsum, or non-purifiedgypsum may have variable purity depending on the source.

A Process for Converting Gypsum into Precipitated Calcium Carbonate

As used herein, “precipitated calcium carbonate” or “PCC” refers to asynthetically manufactured calcium carbonate material that can betailor-made with respect to its compositional forms, purity, morphology,particle size, and other characteristics (e.g. particle sizedistribution, surface area, cubicity, etc.) using various precipitationtechniques and methods. Precipitated calcium carbonate thus differs fromnatural calcium carbonate or natural calcium carbonate-containingminerals (marble, limestone, chalk, dolomite, shells, etc.) or groundcalcium carbonate (natural calcium carbonate which has been ground) interms of both methods of manufacture as well as the variouscompositions/characteristics mentioned above, and which will bedescribed more fully hereinafter.

The method of producing precipitated calcium carbonate (PCC) by use ofcalcined natural calcium carbonate is well-known and widely used in theindustry. Calcining generates calcium oxide from which a precipitatedcalcium carbonate is produced upon consecutive exposure to water andcarbon dioxide. However, the energy consumed in calcining naturalcalcium carbonate is a large part of the production cost. Therefore,converting impure FGD gypsum, a bulk byproduct from power plant energyproduction, or other non-calcined gypsum sources into PCC would providea low energy and economical method for PCC manufacture. The presentdisclosure relates to a process for converting gypsum into precipitatedcalcium carbonate without a calcination step, and controlling themorphology, size, and properties of the precipitated calcium carbonatethus obtained.

Calcium carbonate can be precipitated from aqueous solution in one ormore different compositional forms: vaterite, calcite, aragonite,amorphous, or a combination thereof. Generally, vaterite, calcite, andaragonite are crystalline compositions and may have differentmorphologies or internal crystal structures, such as, for example,rhombic, orthorhombic, hexagonal, scalenohedral, or variations thereof.

Vaterite is a metastable phase of calcium carbonate at ambientconditions at the surface of the earth and belongs to the hexagonalcrystal system. Vaterite is less stable than either calcite oraragonite, and has a higher solubility than either of these phases.Therefore, once vaterite is exposed to water, it may convert to calcite(e.g., at low temperature) or aragonite (at high temperature: ˜60° C.).The vaterite form is uncommon because it is generally thermodynamicallyunstable.

The calcite form is the most stable form and the most abundant in natureand may have one or more of several different shapes, for example,rhombic and scalenohedral shapes. The rhombic shape is the most commonand may be characterized by crystals having approximately equal lengthsand diameters, which may be aggregated or unaggregated. Calcite crystalsare commonly trigonal-rhombohedral. Scalenohedral crystals are similarto double, two-pointed pyramids and are generally aggregated.

The aragonite form is metastable under ambient temperature and pressure,but converts to calcite at elevated temperatures and pressures. Thearagonite crystalline form may be characterized by acicular, needle- orspindle-shaped crystals, which are generally aggregated and whichtypically exhibit high length-to-width or aspect ratios. For instance,aragonite may have an aspect ratio ranging from about 3:1 to about 15:1.Aragonite may be produced, for example, by the reaction of carbondioxide with slaked lime.

In the present disclosure, the methods of producing a PCC compositionmay be varied to yield different polymorphs of calcium carbonate, suchas, for example, vaterite, calcite, aragonite, amorphous calciumcarbonate, or combinations thereof. The methods may be modified byvarying one or more of the reaction rate, the pH of the mixtures, thereaction temperature, the carbonate species present in the reaction(e.g., ammonium carbonate, ammonium bicarbonate), the concentration ofthe different carbonate species present in the reaction (e.g., ammoniumcarbonate and/or ammonium bicarbonate concentrations), the purity of thefeed materials (e.g., purity of the feed gypsum), and the concentrationsof the feed materials (e.g., gypsum and/or carbonate concentrationsand/or seeds and other additives).

Exemplary Methods

In the present disclosure, converting gypsum into precipitated calciumcarbonate is accomplished with Methods A-I, or a combination thereof.Method and process parameter selection enables control of theprecipitated calcium carbonate structure, such as crystalline polymorphand particle size. The following is a general description of the MethodsA-I.

Method A

The method includes:

i. Treating raw gypsum with a mineral acid including, but not limitedto, nitric, sulfuric or phosphoric acid, to consume any unreactedcalcium or magnesium carbonate remaining from the desulfurizationprocess. The amount of mineral acid added to the FGD gypsum isoptionally a molar equivalent of or in excess of the amount of unreactedcarbonate.

ii. Reacting the mineral acid treated FGD gypsum with ammonium carbonateat low temperature ranging from 0-60° C. or from 8-50° C., for 3-300 minor for 5-250 min, to produce calcium carbonate in a vaterite crystalstructure, calcite crystal structure, aragonite crystal structure,amorphous calcium carbonate, or mixtures or blends thereof.

iii. Optionally annealing the resulting calcium carbonate in a dry orwet state to form a desired polymorph or polymorph mixture.

Method B

The method includes:

i. Treating raw gypsum with a mineral acid including, but not limitedto, nitric, sulfuric or phosphoric acid, to consume any unreactedcalcium or magnesium carbonate remaining from the desulfurizationprocess. The amount of mineral acid added to the FGD gypsum is equimolarto the amount of unreacted carbonate.

ii. Adding calcite (or aragonite) from either (ground calcium carbonate)GCC or PCC to the mineral acid treated FGD gypsum as a seed, andreacting with ammonium carbonate at low temperature ranging from 0-60°C. or from 8-50° C., for 3-300 min or for 5-250 min, to produce acalcium carbonate with different dominant morphologies (e.g.,crystalline or amorphous) from that obtained without the added calciumcarbonate. The calcite can be rhombohedral or scalenohedral.

Method C

The method includes:

i. Adding calcium carbonate to raw FGD gypsum to afford a well-definedmixture of calcium carbonate and calcium sulfate.

ii. Reacting the FGD gypsum and calcium carbonate mixture with ammoniumcarbonate at low temperature ranging from 0-60° C. or from 8-50° C., for3-300 min or for 5-250 min, to produce calcium carbonate with adifferent dominant crystal structure from that obtained without theadded calcium carbonate.

Method D

The method includes:

i. Preparing a seeded FGD gypsum by the process of Method B or Method Cabove, where dolomite, dolomitic carbonate, magnesium sulfate, magnesiumhydroxide, titania (TiO₂), silica (SiO₂), or zinc oxide (e.g., ZnO), ormixtures thereof, is added as a seed instead of calcium carbonate.

ii. Reacting the seeded FGD gypsum with ammonium carbonate to producecalcium carbonate in a vaterite crystal structure, calcite crystalstructure, aragonite crystal structure, amorphous calcium carbonate, ormixtures or blends thereof.

According to some embodiments, the seed may result in a hybridmorphology having morphologies related to both the seed morphology andthe PCC morphology.

Method E

The method includes:

i. The process of Methods A, B, C, or D where an additive is added tothe gypsum to yield other defined calcium carbonate polymorphs andparticle sizes, including but not limited to, rhombic or scalenohedralcalcite, vaterite, aragonite, amorphous calcium carbonate, or blendsthereof.

Method F

The method includes

i. The process of Methods A through E wherein the ammonium carbonatecomprises a mixture of ammonium carbonate, ammonium carbamate andammonium bicarbonate, such that the amount of ammonium bicarbonate isgreater than or equal to the ammonium carbamate concentration, and uponreaction yields a calcite or calcite-vaterite blend.

Method G

The method includes:

i. The process of Methods A through E wherein the ammonium carbonatecomprises a mixture of ammonium carbonate, ammonium carbamate andammonium bicarbonate, such that the amount of ammonium bicarbonate isless than or equal to the ammonium carbamate concentration, and uponreaction yields a vaterite or vaterite-calcite blend.

Method H

The method includes:

i. The process of Methods A-G where the ammonium carbonate is producedby the reaction of ammonium hydroxide with CO₂. The ammonium carbonateintroduced to the gypsum slurry is of a tailored pH, and/or excess CO₂is employed to influence the polymorph and particle size obtained.

Method I

The method includes:

i. The process of Methods A through E where a metal carbonate is used inplace of the ammonium carbonate for reaction with the FGD gypsum.

ii. Reacting the FGD gypsum of Methods A through E with the metalcarbonate to produce calcium carbonate in a vaterite crystal structure,calcite crystal structure, or calcite-vaterite-aragonite crystalstructure blend.

Tables 1 and 2 below identify product characteristics obtained fromvarious examples of the foregoing methods.

TABLE 1 Surface Surface Reaction PSD Area Area (StA Reaction ReactionTime Product Geometry (d50), (BET), uptake), Details Temperature(minutes) (FTIR) (SEM) microns D30/d70 × 100 m²/g m²/g 99% pure n/a 20vaterite spherical 5.32 68.49 11.25 10.63 gypsum + “coral” + ammoniumsome rhombic carbonate (DI water) 99% pure 46° C. 10 vaterite spherical5.02 63.29 11.67 10.43 gypsum + “coral” + ammonium some rhombiccarbonate 99% pure 32-37° C.    10 vaterite spherical 3.96 67.11 — 13.51gypsum + “coral” ammonium carbonate 99% pure n/a 95 vaterite spherical4.72 62.50 13.9 12.89 gypsum + “coral” + ammonium some large carbonaterhombic @ room temp 99% pure 20-22° C.    60 vaterite spherical 4.0262.50 14.17 — gypsum + “coral” + ammonium some rhombic carbonate @ roomtemp (redo of Trial 15) 99% pure 32° C. 30 vaterite spherical 3.08 65.79n/a 14.89/14.82 gypsum, 2% “coral” + “pure” some rhombic calciumcarbonate + 2% H2SO4 (excess) w ammonium carbonate 99% pure 35-36° C.   12 calcite rhombic 4.61 60.24 4.95 4.56 gypsum, 2% Supermite + ammoniumcarbonate 99% pure 32° C. 10 calcite rhombic 5.24 59.52 4.15 4.41gypsum, 2% “pure” calcium carbonate + ammonium carbonate 99% pure 30° C.20 calcite rhombic 5.51 59.52 3.65 3.74 gypsum, 2% “pure” calciumcarbonate + ammonium carbonate US gypsum + 36° C. 10 calcite rhombic — —4.65 3.03 ammonium carbonate 99% pure 32° C. 30 vaterite + spherical3.23 59.88 n/a 24.32 gypsum, 2% small amount “coral” + MgCO3 w calciteneedles ammonium carbonate 99% pure 32-34° C.    10 calcite/ spherical4.84 60.98 n/a 6.33 gypsum, 2% vaterite “coral” magnesite ~9:1 wammonium carbonate 99% pure 31° C. 13 vaterite, Rhombic, 2.89 51.00 n/a13.73 gypsum, 2% calcite, spherical dolomitic aragonite “coral” +quicklime + needles ammonium carbonate 99% pure 30° C. 25 calciterhombic 4.91 60.98 n/a 2.62 gypsum, 2% dolomite + ammonium carbonate 99%pure 32° C. 10 vaterite spherical 4.26 68.97 14.25 12.69 gypsum, ~10%“coral” + ammonium some large sulfate rhombic solution + ammoniumcarbonate 99% pure 31-33° C.    10 calcite rhombic - 27.1 72.46 — 2.78gypsum + large ammonium carbonate (amm carb temp fluctuated >46 C.during dissolution, but cooled to 43 C. prior to gypsum addition) Sigma12° C. 120 vaterite + spherical 13.76 71.43 — 15.25/16.04 gypsum + ~8%gypsum “coral” ammonium hydroxide w CO₂ at 12 C. Sigma 29-30° C.    12vaterite elliptical 2.66 43.29 10.71 10.66 gypsum + “coral” + sodiumsome large carbonate rhombic dolomitic 35° C. 40 carbonate + variousshapes: 3.5 26 32.29 n/a quicklime + 15-20% Mg(OH)2 balls, otherammonium carbonate MgSO4 + 25-26° C.    10 MgCO3 undefined 0.74 couldnot be could not be could not be sodium determined determined determinedcarbonate

TABLE 2 Surface Surface Reaction PSD Area Area (StA Reaction ReactionTime Product Geometry (d50), (BET), update), Details Temperature(minutes) (FTIR) (SEM) microns d30/d70 × 100 m2/g m2/g 99% gypsum + 33°C. 10 calcite large 27.1 72.46 n/a 2.78 ammonium rhombic carbonate (atelevated ammonium carbonate temperature) 99% pure 36° C. 12 calciteRhombic 4.61 60.24 4.95 4.56 gypsum, 2% calcite + ammonium carbonate 99%pure 34° C. 10 calcite w Rhombic 4.84 60.24 n/a 6.33 gypsum, 2% smallmagnesite + amount of ammonium vaterite carbonate 99% pure 35° C. 25calcite Rhombic 4.91 60.24 n/a 2.62 gypsum, 2% dolomite + ammoniumcarbonate

In the present disclosure, the term “reaction” may refer to any completeor partial reaction. A partial reaction refers to any reaction wheresome amount of a reagent or substrate remains in the reaction mixtureafter the reaction takes place.

In regards to methods A-I, precipitation of the PCC may be influenced orcontrolled by one or more of the reaction rate, pH, the ionic strength,reaction temperature, carbonate species present in the reaction, seedspecies composition, seed species concentration, purity of the feedmaterials (e.g., gypsum), concentration of the feed materials, ratio ofthe feed materials, or aging of the reaction components.

In terms of methods A-I, the pH of the reacting mixture may becontrolled. In one embodiment, the reacting mixture may be acidic (pHless than 6.5), neutral (pH 6.5-7.5), or basic (pH greater than 7.5). Inregards to methods A-I, the ionic strength of the reacting mixture mayalso be controlled. The ionic strength, I, of a solution is a functionof the concentration of all ions present in that solution.

$I = {\frac{1}{2}{\sum\limits_{i = 1}^{n}\; {c_{i}z_{i}^{2}}}}$

where c_(i) is the molar concentration of ion i (M, mol/L), z_(i) is thecharge number of that ion, and the sum is taken over all ions in thesolution. In one embodiment, the ionic strength is controlled by thestoichiometry of ionizable reactants. In another embodiment, the ionicstrength is controlled by the addition of ionic additives. These ionicadditives may be a participating reactant, a spectator ion (i.e. anon-participating reactant), and/or a total ionic strength adjustmentbuffer. In another embodiment, the ionic strength is controlled by theuse of deionized (DI) water.

In regards to methods A-I, a solvent may be added to gypsum to form agypsum solution, slurry or suspension prior to reacting with thecarbonate source. Suitable solvents that may be used for forming agypsum solution, slurry, or suspension include aprotic polar solvents,polar protic solvents, and non-polar solvents. Suitable aprotic polarsolvents may include, but are not limited to, propylene carbonate,ethylene carbonate, butyrolactone, acetonitrile, benzonitrile,nitromethane, acetonitrile, nitrobenzene, sulfolane, dimethylformamide,N-methylpyrrolidone, or the like. Suitable polar protic solvents mayinclude, but are not limited to, water, nitromethane, and short chainalcohols. Suitable short chain alcohols may include, but are not limitedto, one or more of methanol, ethanol, propanol, isopropanol, butanol, orthe like. Suitable non-polar solvents may include, but are not limitedto, cyclohexane, octane, heptane, hexane, benzene, toluene, methylenechloride, carbon tetrachloride, or diethyl ether. Co-solvents may alsobe used. In a certain embodiment, the solvent added to gypsum is water.Gypsum is moderately water-soluble (2.0-2.5 g/l at 25° C.). Therefore,to form a gypsum solution, enough water is added to fully dissolve allof the gypsum prior to reaction. To form a slurry or suspension, anamount of water is added to partially dissolve the gypsum, such thatsome of the gypsum is fully dissolved and some of the gypsum remains insolid form. In another embodiment, water is added to gypsum to form aslurry, wherein the percent of solids in the slurry is 10-50%, 20-40%,or 30-35%. In methods A-I, the concentration of the reacting mixture isalso controlled. In a certain embodiment, the concentration iscontrolled by the addition or subtraction of water from the reactingsolution, mixture, or slurry.

In terms of methods A-I, the mineral acid, ammonium carbonate, calcite,aragonite, calcium carbonate, dolomite, ammonium bicarbonate, ammoniumcarbamate, ammonium hydroxide, carbon dioxide, or any other additive orcombination thereof, may be added to the gypsum in bulk, portion-wise,or by a slow-addition process to control the PCC productcharacteristics. The rate of addition of these components also controlsthe reacting mixture concentration. In terms of methods A-I, the mineralacid, ammonium carbonate, calcite, aragonite, calcium carbonate,dolomite, ammonium bicarbonate, ammonium carbamate, ammonium hydroxide,carbon dioxide, or any other additive or carbonate source or combinationthereof is added as a solution, a solid, a suspension or slurry, a gas,or a neat liquid. In terms of adding a gas, the gas may be bubbled intoa solution to an effective concentration, or may be used to purge orpressurize the reaction vessel until a desired effective concentrationis reached.

In one embodiment, the carbonate source is selected from the groupconsisting of ammonium carbonate, ammonium bicarbonate, ammoniumcarbamate, calcium carbonate, dolomite, a metal carbonate, and carbondioxide, wherein the metal carbonate comprises a carbonate orbicarbonate anion and at least one cation selected from the groupconsisting of sodium, calcium, cobalt, copper, potassium, ammonium,chromium, iron, aluminum, tin, lead, magnesium, silver, titanium,vanadium, zinc, lithium, nickel, barium, strontium, and hydronium. In acertain embodiment, water is added to the carbonate source to form aslurry prior to the reaction with gypsum. The carbonate source slurry isthen added to the gypsum to give a molar ratio of reaction ofgypsum:carbonate source of 1:1.1 to 1:5, 1:1.3 to 1:2.5, or 1:1.5 to1:2. The carbonate selected should, after reaction with the gypsum,yield a sulfate product with higher solubility than the calciumcarbonate generated. Therefore, the generated sulfate may be separatedfrom the calcium carbonate precipitate by removal of the aqueous phasefrom the reaction slurry. Exemplary metal carbonates include sodiumcarbonate and magnesium carbonate. The sulfate product can be treated asneeded, and used for an appropriate, separate application. For example,if ammonium carbonate is used in the reaction, ammonium sulfate will begenerated, which can be separated and used in applications such asfertilizer. In addition, a portion can be fed into the starting gypsumslurry to aid in control of the reaction rate, and consequently, controlthe PCC produced. After separating the PCC slurry from the aqueoussolution to form a PCC cake, the cake can be washed with water to removeremaining sulfate. The carbonate source can be pre-formed or generatedduring the reaction. For example, CO₂ may be bubbled with ammonia gas togenerate ammonium carbonate used for the reaction. In general, ammoniumcarbonate exists as a mixed salt comprising a mixture of ammoniumcarbonate, ammonium carbamate, and ammonium bicarbonate. The amount ofeach species may depend on the reaction conditions used to manufacturethe ammonium carbonate. Furthermore, ammonium carbamate quickly convertsto ammonium carbonate in the presence of water. In general, ammoniumbicarbonate dissolves slower and reacts slower with gypsum than ammoniumcarbamate or ammonium carbonate.

The PCC production process of methods A-I of the present disclosure aimsto produce only one form of PCC. However, a small amount of analternative polymorph is often present, and can be readily tolerated inmost end uses. Thus, the PCC compositions comprising mixtures ofcrystalline forms (e.g., aragonite and calcite) can be readily employedin coating formulations. Even in the case of PCC compositionspredominantly comprising one form (predominately vaterite, for example),the compositions are likely to contain a small amount of at least oneother crystal PCC structure (e.g., calcite). As a result, the PCCcompositions of the present disclosure may optionally comprise at leastone second PCC form that differs from the main PCC form.

In some embodiments, the size, surface area, and cubicity of the PCCproducts may be influenced by feed concentrations or aging of thereaction components. For example, a lower feed concentration may resultin a larger particle size distribution. A larger particle sizedistribution may have a lower surface area. Aging, for example, mayreduce the surface area of the PCC or improve the cubicity of the PCCparticles. According to some embodiments, the aging may convert some orall of a polymorph to a different polymorph. For example, aging mayconvert a vaterite phase to calcite. According to some embodiments,including ammonium sulfate in a gypsum slurry feed may aid incontrolling the PCC polymorph and particle size.

In certain embodiments of the present disclosure, a stage of drying thePCC product may also be carried out in any of methods A-I subsequent todewatering. The drying of the product may also contribute to theresulting crystal product polymorph. In certain embodiments of thepresent disclosure, the PCC reaction product is a first compositionafter the reaction, prior to drying, with a solids content of at least70%. The PCC reaction product may convert to a second composition afterthe drying stage. The drying stage may convert any amorphous PCC productof a first composition to a crystalline polymorph of a secondcomposition (and different drying methods may make differentpolymorphs). The product of a first composition may be aged and seeded.A dried product may also be aged. Similar to the drying process, agingmay also change the polymorph composition. The reaction to form PCC, theseeding, the drying, and the aging may all be employed in a batchprocess, or a continuous process (e.g. in a tubular reactor with inlinestatic mixers or cascade mixers). In one embodiment, the drying isperformed at a temperature range of 30-150C for 1-15 hours.

In some embodiments, the addition of additives or seed materials mayaffect the structure of the PCC. For example, adding citric acid to thePCC formation step may increase the surface area of a formed PCCproduct. Altering the pH, such as through the use of an acidic additive,such as an acid (e.g., phosphoric acid), may be used to control or varythe shape, particle size, or surface area of the PCC, and in particularto vary the morphology of a PCC. In some embodiments, the seedcomposition may be used to control the resulting PCC morphology. Forexample, using greater than about 5 wt % coarse scalenohedral PCC(relative to the weight of the feed material) as a seed material mayyield a larger or coarser PCC product, and may result in a greatersurface area. For example, using less than about 5% of a finerhombohedral PCC as a seed material yields a PCC product with a finercrystal size within a PCC aggregate, whereas greater than about 5% ofthe fine rhombohedral PCC seed material yields a finer-sized aggregateof the PCC produced. Further, under seeding conditions where a purecalcite seed (where dolomite or magnesium levels are <2%) is added tothe reacting mixture, the resulting PCC product is formed with a rhombicgeometry. Similarly, seeding with magnesite or dolomite also yieldsrhombic PCC.

In the present disclosure, a “hybrid structure” refers to a PCCcomponent bound to at least a portion of a surface of a seed component.For example, the PCC component may be chemically bound to the seedcomponent, such as, for example, through ionic, coordinate covalent(dative), or van der Waals bonds. According to some embodiments, the PCCcomponent may physically bond or attach to the seed component. Accordingto some embodiments, the PCC component may be adsorbed or physisorbed tothe seed component. According to some embodiments, the PCC component mayform a carbonate layer over the seed component during the carbonateaddition step. For example, the PCC component may form a carbonatelayer, shell, or coating that covers at least a portion of, majority of,or substantially all of the seed component. According to someembodiments, the PCC component may coat, enclose, or encapsulatesubstantially all of the seed component. According to some embodiments,the hybrid structure may include a PCC component, a seed component,and/or an interfacial component. The interfacial component may be, forexample, a boundary region between the PCC component and the seedcomponent. The interfacial component may include a chemical compositioncontaining elements of the carbonate component and the second component.For example, when the hybrid structure includes a calcium carbonate asthe PCC component and a magnesium carbonate as the seed component, aninterfacial region may include calcium and/or magnesium diffusing intothe other component, or a region containing a mixture of calciumcarbonate and magnesium carbonate. An interfacial region may occur, forexample, upon thermal treatment (e.g., sintering) of the hybridstructure.

A structure described as “amorphous” herein refers to no short or longchain order and a crystalline structure refers to at least some level oforder. Materials that may be described as semi-crystalline may thereforebe considered crystalline in the present disclosure. The products hereinare typically not 100% crystalline or 100% amorphous or non-crystalline,but rather exist on a spectrum between these points. In someembodiments, the PCC may be predominantly amorphous or a combination ofan amorphous phase and a crystalline phase (such as calcite, vaterite,or aragonite).

“Produced directly” as used herein, refers to a process where a productpolymorph (e.g. calcite) is formed without the formation of anintermediate polymorph (e.g. vaterite) that is isolated, and in a secondindependent step, converted into the product polymorph using aprocessing technique mentioned herein (e.g. wet aging). In other words,“produced directly” refers to a process whereby the product is formed inone reaction operation. An example of a reaction product that is not“produced directly” may include forming an intermediate polymorph usinga reaction method referred to herein, and subsequently isolating theintermediate polymorph, and subjecting it to a processing condition thatconverts the intermediate polymorph into a different product polymorph.

The gypsum used in the present process may be purified gypsum orunpurified gypsum. In one embodiment, the gypsum is filtered, sieved, orcentrifuged to remove impurities prior to the reacting.

Exemplary Processes for Converting Gypsum into Calcite

According to a another aspect, the present disclosure relates to aprocess for converting gypsum into precipitated calcium carbonate,involving reacting a mixture comprising gypsum and a seed, a mineralacid, or both with at least one carbonate source to produce precipitatedcalcium carbonate. The reactants and the seed and/or the mineral acidcontrol the crystalline polymorph and/or particle size of theprecipitated calcium carbonate, the precipitated calcium carbonate is inthe form of calcite, and the calcite is produced directly from thereactants without conversion from a vaterite polymorph.

A. In one embodiment, a calcite polymorph is produced directly when themineral acid is citric acid, nitric acid, or phosphoric acid. Inalternate embodiments, the mineral acid is an acid with a pKa less thanor equal to 3. In one embodiment, the gypsum starting material mayinclude carbonate impurities, and, in this scenario, the mineral acid isadded with a molar equivalence that is greater than or equal to themolar equivalence of the carbonate impurities in the gypsum. In certainembodiments, the mineral acid may be present in an amount ranging from0.1 wt % to 20 wt %, or 0.5 wt % to 10 wt %, or 1 wt % to 5 wt % basedon the dry weight of gypsum.

B. In method B, a calcite PCC product may be formed when the gypsum istreated with a mineral acid as described in reference to method A andseeded with a calcite seed. In one embodiment, less than 25% by weightof a calcium carbonate seed is added to the gypsum, for example lessthan 10%, less than 5%, or less than 1% by weight based on the gypsum.For instance, the seed may be present in an amount ranging from 0.1% to25%, or 0.5 to 15%, or 1% to 10% by weight based on the gypsum. In oneembodiment, the PCC produced has a dominant crystal polymorph consistentwith calcite, with a geometry comprising rhombic. In another embodiment,the PCC produced has a PSD (d₅₀) ranging from 1-28 microns. In anotherembodiment, the PCC has a steepness (d₃₀/d₇₀×100) in a range from30-100, or 53-71, or 59-63. In another embodiment, the PCC has a surfacearea (BET and/or stearic acid uptake) ranging from 1-30, or from 3-9m²/g. According to some embodiments, the PCC may have a relatively steepparticle size distribution, for example, a steepness greater than about46. According to some embodiments, the PCC may have a relatively broadparticle size distribution, for example, a steepness less than about 40.

C. In one embodiment, a calcite polymorph PCC is produced when the seedis a calcite seed. In some embodiments, at least 25% by weight ofcalcium carbonate is added to the gypsum, at least 10%, at least 5%, atleast 2%, or at least 1% by weight based on the gypsum. For instance,the seed may be present in an amount ranging from 1% to 25%, or 2 to30%, or 5% to 40% by weight based on the gypsum. In one embodiment, thePCC produced has a dominant crystal polymorph consistent with calcite,with a geometry comprising rhombic. In another embodiment, the PCC has asurface area ranging from 0.1-8, or from 2.5-30 m²/g.

D. The seed may also be at least one selected from the group consistingof dolomite, dolomitic carbonate, magnesium sulfate, magnesiumhydroxide, titania, silica, and zinc oxide. For example, the seed may bedolomitic calcium carbonate. In some embodiments, the PCC produced mayhave a crystal geometry including needle forms of rhombic calcite, aswell as other forms. Further, the PCC may have a hybrid structure whenseeded with a non-PCC seed material, such as, for example, titania,silica, zinc oxide, or mixtures thereof. In some embodiments, the gypsummay be seeded with magnesium sulfate and/or magnesium hydroxide insteadof calcium carbonate.

E. The additive may be, but is not limited to a buffer, a dispersant, athickener, an anticaking agent, a defoamer, a rheology agent, a wettingagent, a crystal seed, a co-solvent, a brightness enhancer, or any agentthat affects crystal morphology/geometry of the product. Examples ofadditives include, but are not limited to, citric acid, phosphoric acid,a sugar, BaCl₂, MgO, MgCO₃, H₂SO₄, H₃PO₄, HCl, various phosphates,sodium hexametaphosphate, ammonium sulfate, sodium thiosulfate, and NO₃compounds. Examples of brightness enhancers include, but are not limitedto, fluorescent brightening agents. According to some embodiments, whenthe additive is an acid, such as, for example, citric acid, the surfacearea of a resulting PCC morphology may be increased. The selection ofthe acid, such as, for example, phosphoric acid, may be used in varyingamounts to control the shape, particle size, and/or surface area of thePCC. In one embodiment, a calcite polymorph is produced when the mixturefurther comprises citric acid, phosphoric acid, ammonium sulfate, orsodium thiosulfate. In one embodiment, the weight % of the additiveranges from 0.1% to 20%, or 0.5% to 10%, or 1% to 6% relative to thegypsum. In some embodiments, ammonium sulfate is added to the reactionmixture to control the reaction rate. In some embodiments, sodiumthiosulfate is added instead of ammonium sulfate. For example, theammonium sulfate may be added to a gypsum slurry. The concentration ofammonium sulfate may be varied to control the PCC polymorph type andparticle size.

F. The carbonate source may be at least one selected from the groupconsisting of ammonium carbonate, ammonium bicarbonate, ammoniumcarbamate, calcium carbonate, dolomite, a metal carbonate, and carbondioxide. When a mixture of ammonium carbonate is in solution withgypsum, and the reaction takes place in solution, the PCC product tendsto be calcite. In one embodiment, the carbonate source is a carbonatemixture of ammonium carbonate, ammonium carbamate, and ammoniumbicarbonate, and the amount of ammonium bicarbonate is greater than orequal to the amount of ammonium carbamate or ammonium carbonate in thecarbonate mixture. In one embodiment, ammonium bicarbonate is added tothe ammonium carbonate (or vice versa) to generate a mixture, and themixture is then added to the gypsum. In another embodiment, CO₂ gas isbubbled into a slurry containing ammonium hydroxide, and the bubblingresults in the formation of ammonium carbonate, and ammonium bicarbonateand/or ammonium carbamate in situ, and the resulting mixture of ammoniumcarbonate, ammonium carbamate and ammonium bicarbonate is then added tothe gypsum.

In certain embodiments, the reaction temperature may be equal to orgreater than 30° C. and the polymorph formed is calcite.

In other embodiments, the gypsum is a natural gypsum and the polymorphformed is a calcite and/or vaterite product. For instance, the calciumcarbonate product may comprise at least 30% calcite and vaterite.

In certain embodiments, the reaction is carried out at a pH equal to orgreater than 10 and the polymorph formed is calcite.

H. In one embodiment, the carbonate source is carbon dioxide and thecarbon dioxide is reacted with ammonia or ammonium hydroxide prior to orduring reacting with the mixture comprising gypsum and a seed, a mineralacid, or both. The pH of the mixture is tailored to a pH equal to orgreater than 10, which may result in the formation of a calcitepolymorph. In the process, the pH can be adjusted by adjusting theconcentration of the carbon dioxide or the ammonia. In the presentdisclosure, the amount of carbonate source added may be greater than theamount of gypsum present in the mixture, where the molar ratio of thegypsum to the carbonate source ranges from about 1:1.1 to 1:5, 1:1.3 to1:2.5, or from about 1:1.5 to 1:2. The carbon dioxide can be pure carbondioxide gas, flue gas containing 15-90% carbon dioxide gas, or flue gaswith enriched carbon dioxide gas (e.g., greater than 90% CO₂). In oneembodiment, the FGD gypsum is mixed with ammonia prior to the additionof CO₂. Ammonium hydroxide may be pre-formed by addition of ammonia towater, and the ammonium hydroxide may be fed into slurried gypsum priorto addition of CO₂. Alternatively, ammonium carbonate may be fullygenerated, then introduced to the slurried gypsum for reaction. Reactingammonium hydroxide with CO₂ at room temp to 40° C. gives a mixture ofammonium carbonate and ammonium bicarbonate, which may react asanticipated with seeded gypsum to produce calcite. In presence ofgypsum, ammonium hydroxide with CO₂ yields a mixture of ammoniumcarbonate and ammonium bicarbonate, which begins to react with gypsumand yield ammonium sulfate during ammonium bicarbonate and ammoniumcarbonate generation. In an alternative embodiment, ammonia and CO₂ arefirst mixed and reacted, and then the reacted mixture is mixed with theFGD gypsum. In one embodiment, the CO₂ is added by bubbling intosolution. In an alternative embodiment, CO₂ is added as dry ice. Duringthe preparation, the nucleation rate and crystal size of calciumcarbonate can be controlled through controlling of the reaction time andtemperature. In a certain embodiment, the carbon dioxide, or carbondioxide equivalent is equimolar or greater to the gypsum reactant. Thereaction time may be 0.2-10 hours, or 0.5-3 hours, and the temperaturemay be in a range from 8-90° C., or from 10-98 C. According to someembodiments, a CO₂-containing gas, such as a flue gas, may becontinuously added during the reaction period with the ammonia.According to some embodiments, the addition of a CO₂-containing gas maybe stopped during the reaction period with the ammonia. When the CO₂addition is stopped, it may be optionally restarted prior to afiltration step. According to some embodiments, the reaction productsmay be stored before separating the carbonate from ammonium sulfate toallow for ripening of the reaction products. The ripening could beperformed with or without the addition of CO₂ during the storage.According to some embodiments, the CO₂ may be added after the conversionto calcium carbonate and ammonium sulfate. According to someembodiments, the CO₂ may be added after isolating the calcium carbonate.According to some embodiments, the introduction of CO₂, such as, forexample, after isolating the calcium carbonate or after a reslurryingstep, may be used to control the particle size of the calcium carbonate.

I. In an alternative embodiment, the carbonate source is an alkali metalcarbonate, which is sodium, potassium, cesium, lithium, rubidium,francium. In one embodiment, the metal of the metal carbonate is amonovalent ion (e.g., an alkali metal). In one embodiment, the PCCproduced may have a crystal geometry including needle forms ofaragonite, rhombic calcite, and other forms. In one embodiment, themetal of the metal carbonate is a divalent ion, such as, for example,magnesium, strontium, beryllium, barium, or radium. Magnesium carbonatemay also be yielded under conditions where magnesium cation is presentin the gypsum or in the metal carbonate (e.g. magnesium carbonate,dolomite, etc.).

The process for converting gypsum into precipitated calcium carbonatefurther includes processing the precipitated calcium carbonate by atleast one method selected from the group consisting of dewatering,drying, ageing, surface treating, size reducing, and beneficiating.Processing PCC with a calcite polymorph may change the aforementionedproperties of the calcite. However, the processing does not convertcalcite into another polymorph.

Exemplary Processes for Converting Gypsum into Aragonite

According to a first aspect, the present disclosure relates to a processfor converting gypsum into precipitated calcium carbonate, involvingreacting a mixture comprising gypsum and a seed, a mineral acid, or bothwith at least one carbonate source to produce precipitated calciumcarbonate. The reactants and the seed and/or the mineral acid controlthe crystalline polymorph and/or particle size of the precipitatedcalcium carbonate, the precipitated calcium carbonate is in the form ofaragonite, and the aragonite is produced directly from the reactionwithout conversion from a vaterite polymorph.

C. In one embodiment, an aragonite polymorph PCC is produced when theseed is aragonite or a blended seed. The blended seed may comprisemagnesium carbonate and calcium carbonate, for instance, blended at aratio of 5:1 or more preferably 3:1. In some embodiments, at least 10%by weight of seed is added to the gypsum, at least 5%, at least 2%, orat least 1% by weight based on the gypsum. For instance, the seed may bepresent in an amount ranging from 1% to 25%, or 2 to 30%, or 5% to 40%by weight based on the gypsum. In one embodiment, the PCC produced has adominant crystal polymorph consistent with aragonite. In anotherembodiment, the PCC has a surface area (BET and/or stearic acid uptake)ranging from 2 to 30 m²/g, or from 5 to 15 m²/g, or from 2 to 8 m²/g.

D. The seed may also be at least one selected from the group consistingof dolomitic carbonate, magnesium sulfate, magnesium hydroxide, titania,silica, strontium and zinc oxide. For example, the seed may be dolomiticcalcium carbonate of high magnesium content. Further, the PCC may have ahybrid structure when seeded with a non-PCC seed material, such as, forexample, titania, silica, zinc oxide, strontium or mixtures thereof. Insome embodiments, the gypsum may be seeded with magnesium sulfate and/ormagnesium hydroxide instead of a carbonate.

E. The additive may be, but is not limited to a buffer, a dispersant, athickener, an anticaking agent, a defoamer, a rheology agent, a wettingagent, a crystal seed, a co-solvent, a brightness enhancer, or any agentthat affects crystal morphology/geometry of the product. Examples ofadditives include, but are not limited to, citric acid, phosphoric acid,a sugar, BaCl₂, MgO, MgCO₃, H₂SO₄, H₃PO₄ HCl, various phosphates, sodiumhexametaphosphate, ammonium sulfate, sodium thiosulfate, and NO₃compounds. Examples of brightness dampeners include, but are not limitedto, Fe₂O₃, MnO, and Pb⁺². According to some embodiments, when theadditive is an acid, such as, for example, citric acid, the surface areaof a resulting PCC morphology may be increased. The selection of theacid, such as, for example, phosphoric acid, may be used in varyingamounts to control the shape, particle size, and/or surface area of thePCC. In one embodiment, the weight % of the additive ranges from 0.1% to25%, or 0.5 to 15%, or 1% to 10% relative to the gypsum. In someembodiments, ammonium sulfate is added to the reaction mixture tocontrol the reaction rate. In some embodiments, sodium thiosulfate isadded instead of ammonium sulfate. For example, the ammonium sulfate maybe added to a gypsum slurry. The concentration of ammonium sulfate maybe varied to control the PCC polymorph type and particle size.

F. The carbonate source may be at least one selected from the groupconsisting of ammonium carbonate, ammonium bicarbonate, ammoniumcarbamate, calcium carbonate, dolomite, a metal carbonate, and carbondioxide. In one embodiment, ammonium bicarbonate is added to theammonium carbonate (or vice versa) to generate a mixture, and themixture is then added to the gypsum. In another embodiment, CO₂ gas isbubbled into a slurry containing ammonium hydroxide, and the bubblingresults in the formation of ammonium carbonate, and/or ammoniumbicarbonate and/or ammonium carbamate in situ, and the resulting mixtureof ammonium carbonate, ammonium carbamate and ammonium bicarbonate isthen added to the gypsum.

H. In one embodiment, the carbonate source is carbon dioxide and thecarbon dioxide is reacted with ammonia or ammonium hydroxide prior to orduring reacting with the mixture comprising gypsum and a seed, a mineralacid, or both. In the process, the pH can be adjusted by adjusting theconcentration of the carbon dioxide or the ammonia. In the presentdisclosure, the amount of carbonate source added may be greater than theamount of gypsum present in the mixture, where the molar ratio of thegypsum to the carbonate source ranges from about 1:1.1 to 1:5, 1:1.3 to1:2.5, or from about 1:1.5 to 1:2. The carbon dioxide can be pure carbondioxide gas, flue gas containing 15-90% carbon dioxide gas, or flue gaswith enriched carbon dioxide gas (e.g., greater than 90% CO₂). In oneembodiment, the FGD gypsum is mixed with ammonia prior to the additionof CO₂. Ammonium hydroxide may be pre-formed by addition of ammonia towater, and the ammonium hydroxide may be fed into slurried gypsum (orvice versa) prior to addition of CO₂. Alternatively, ammonium carbonateor ammonium carbonate with ammonium bicarbonate may be fully generated,then introduced to the slurried gypsum for reaction. In the presence ofgypsum, ammonium hydroxide with CO₂ yields ammonium bicarbonate andammonium carbonate, which begins to react with gypsum and yield ammoniumsulfate during ammonium bicarbonate and ammonium carbonate generation.In an alternative embodiment, ammonia and CO₂ are first mixed andreacted, and then the reacted mixture is added to the FGD gypsum. In oneembodiment, the CO₂ is added by bubbling into solution. In analternative embodiment, CO₂ is added as dry ice. During the preparation,the nucleation rate and crystal size of calcium carbonate can becontrolled through control of the reaction time and temperature. In acertain embodiment, the carbon dioxide, or carbon dioxide equivalent isequimolar or greater to the gypsum reactant. The reaction time may be0.2-10 hours, or 0.5-3 hours, and the temperature may be in a range from8-90° C., or from 10-98° C. According to some embodiments, aCO₂-containing gas, such as a flue gas, may be continuously added duringthe reaction period with the ammonia. According to some embodiments, theaddition of a CO₂-containing gas may be stopped during the reactionperiod with the ammonia. When the CO₂ addition is stopped, it may beoptionally restarted prior to a filtration step. According to someembodiments, the reaction products may be stored before separating thecarbonate from ammonium sulfate to allow for ripening of the reactionproducts. The ripening could be performed with or without the additionof CO₂ during the storage. According to some embodiments, the CO₂ may beadded after the conversion to calcium carbonate and ammonium sulfate.According to some embodiments, the CO₂ may be added after isolating thecalcium carbonate. According to some embodiments, the introduction ofCO₂, such as, for example, after isolating the calcium carbonate orafter a reslurrying step, may be used to control the particle size ofthe calcium carbonate.

I. In an alternative embodiment, the carbonate source is an alkali metalcarbonate, which is sodium, potassium, cesium, lithium, rubidium,francium. In one embodiment, the metal of the metal carbonate is amonovalent ion (e.g., an alkali metal). In one embodiment, the PCCproduced may have a crystal geometry including needle forms ofaragonite, and other forms. In one embodiment, the metal of the metalcarbonate is a divalent ion, such as magnesium. Magnesium carbonate mayalso be yielded under conditions where magnesium cation is present inthe gypsum or in the metal carbonate (e.g. magnesium carbonate,dolomite, etc.).

The process for converting gypsum into precipitated calcium carbonatefurther includes processing the precipitated calcium carbonate by atleast one method selected from the group consisting of dewatering,drying, ageing, surface treating, size reducing, and beneficiating.

Exemplary Processes for Converting Gypsum into Vaterite

According to a second aspect, the present disclosure relates to aprocess for converting gypsum into precipitated calcium carbonate,including providing i) gypsum and ii) a seed, or at least one processcondition selected from the group consisting of a reaction temperaturebetween 10 and 60° C., or between 18 to 45° C., or more preferably 25 to35° C.; and reacting the gypsum with at least one carbonate source toproduce precipitated calcium carbonate in the form of vaterite. Thereactants and the seed and/or process conditions control the particlesize of the vaterite.

The PCC produced has a dominant crystal polymorph consistent withvaterite, with a geometry comprising spherical “coral” as well as somerhombic. In some embodiments, the vaterite PCC may have a flower-shapedgeometry, a rose-shaped geometry, a needle-shaped geometry, aball-shaped or spherical-shaped geometry, or a hexagonal geometry. Thegeometry or structure of the vaterite may be varied by varying one ormore of the reaction rate, pH, reaction temperature, or purity of thefeed gypsum. For example, a feed of high-purity gypsum (e.g., 99%)yields vaterite with a ball-shaped geometry, whereas co-generating anammonia-based carbonate precursor and the PCC tends to yield a moreflower-shaped vaterite. According to some embodiments, ball-shapedvaterite PCC is produced with pre-formed ammonia-based carbonates andlower purity gypsum during the PCC reaction. The PCC produced has a PSD(d₅₀) ranging from 0.1-30, or from 1.0-20, or from 2.0-12.0, or from3.0-7.0 microns. In another embodiment, the PCC has a steepness(d₃₀/d₇₀×100) ranging from 30-100, or 50-100, or 56-83, or 59-71. Inanother embodiment, the PCC has a surface area (BET and/or stearic aciduptake) ranging from 5-75 m²/g, or from 5-20 m²/g, or from 7-15 m²/g.

In other embodiments, a reaction temperature of less than 30° C. resultsin a vaterite polymorph.

E. The additive may be, but is not limited to a buffer, a dispersant, athickener, an anticaking agent, a defoamer, a rheology agent, a wettingagent, a crystal seed, a co-solvent, a brightness enhancer or dampener,or any agent that affects crystal morphology/geometry of the product.Examples of additives include, but are not limited to, citric acid,phosphoric acid, a sugar, BaCl₂, MgO, MgCO₃, H₂SO₄, H₃PO₄ HCl, variousphosphates, sodium hexametaphosphate, ammonium sulfate, sodiumthiosulfate, and NO₃ compounds. Examples of brightness dampenersinclude, but are not limited to, Fe₂O₃, MnO, and Pb⁺² and other leadcompounds. According to some embodiments, when the additive is an acid,such as, for example, citric acid, the surface area of a resulting PCCmorphology may be increased. The selection of the acid, such as, forexample, phosphoric acid, may be used in varying amounts to control theshape, particle size, and/or surface area of the PCC. In one embodiment,the additive is ammonium sulfate, and ammonium sulfate is present in themixture from 0.5 wt/vol % to 50 wt/vol %, or 2 wt/vol % to 35 wt/vol %,or 4% to 20% by weight. In some embodiments, ammonium sulfate is addedto the reaction mixture to control the reaction rate. In someembodiments, sodium thiosulfate is added instead of ammonium sulfate.For example, the ammonium sulfate may be added to a gypsum slurry. Theconcentration of ammonium sulfate may be varied to control the PCCpolymorph type and particle size. Alternatively, the organic acid iscitric acid, and the wt % of citric acid in the mixture is greater thanor equal to 0.1%, greater than or equal to 10%, or greater than or equalto 25% relative to the weight of gypsum.

G. The carbonate source is at least one selected from the groupconsisting of ammonium carbonate, ammonium bicarbonate, ammoniumcarbamate, calcium carbonate, dolomite, a metal carbonate, and carbondioxide. In one embodiment, the carbonate source is a carbonate mixtureof ammonium carbonate, ammonium carbamate, and ammonium bicarbonate, andthe amount of ammonium bicarbonate is less than the amount of ammoniumcarbamate or ammonium carbonate in the carbonate mixture. In general,under conditions in which the reaction between the carbonate source andgypsum takes place in a slurry, the PCC yielded is vaterite. In oneembodiment, ammonium bicarbonate is added to the ammonium carbonate (orvice versa) to generate a mixture, and the mixture is then added to thegypsum. In another embodiment, CO₂ gas is bubbled into a slurrycontaining ammonium hydroxide, and the bubbling results in the formationof ammonium carbonate and/or ammonium carbamate, and ammoniumbicarbonate in situ, and the resulting mixture of ammonium carbonate,ammonium carbamate and ammonium bicarbonate is then added to the gypsum.

H. In yet another embodiment, the carbonate source is carbon dioxide andthe carbon dioxide is reacted with ammonia or ammonium hydroxide priorto or during reacting with the mixture comprising gypsum and a seed, amineral acid, or both. The pH of the mixture is tailored to a pH of lessthan 10, which results in formation of a vaterite polymorph. The carbondioxide can be pure carbon dioxide gas, flue gas containing 15-90%carbon dioxide gas, or flue gas with enriched carbon dioxide gas (e.g.,greater than 90% CO₂). In one embodiment, the FGD gypsum is mixed withammonia prior to the addition of CO₂. Ammonium hydroxide may bepre-formed by addition of ammonia to water, and the ammonium hydroxidemay be fed into slurried gypsum prior to addition of CO₂. In analternative embodiment, ammonia and CO₂ are first mixed and reacted, andthen the reacted mixture is added to the FGD gypsum. Reacting ammoniumhydroxide with CO₂ at room temp or up to at least 40° C. gives a mixtureof ammonium carbonate and ammonium bicarbonate, which reacts asanticipated with unseeded gypsum to give vaterite. Alternatively,ammonium carbonate may be fully generated, then introduced to theslurried gypsum for reaction. In presence of gypsum, ammonium hydroxidewith CO₂ yields ammonium carbonate and ammonium bicarbonate, whichbegins to react with gypsum and yield ammonium sulfate during ammoniumbicarbonate and ammonium carbonate generation. In one embodiment, theCO₂ is added by bubbling into solution. In an alternative embodiment,CO₂ is added as dry ice. During the preparation, the nucleation rate andcrystal size of calcium carbonate can be controlled through controllingof the reaction time and temperature. In a certain embodiment, thecarbon dioxide, or carbon dioxide equivalent is equimolar or greater tothe gypsum reactant. The reaction time is 0.2-10 hours, or 0.5-3 hours,and the temperature is in a range from 8-90° C., or from 10-98° C.According to some embodiments, a CO₂-containing gas, such as a flue gas,may be continuously added during the reaction period with the ammonia.According to some embodiments, the addition of a CO₂-containing gas maybe stopped during the reaction period with the ammonia. When the CO₂addition is stopped, it may be optionally restarted prior to afiltration step. According to some embodiments, the reaction productsmay be stored before separating the carbonate from ammonium sulfate toallow for ripening of the reaction products. The ripening could beperformed with or without the addition of CO₂ during the storage.According to some embodiments, the CO₂ may be added after the conversionto calcium carbonate and ammonium sulfate. According to someembodiments, the CO₂ may be added after isolating the calcium carbonate.According to some embodiments, the introduction of CO₂, such as, forexample, after isolating the calcium carbonate or after a reslurryingstep, may be used to control the particle size of the calcium carbonate.

I. In an alternative embodiment, the carbonate source is an alkali metalcarbonate, such as sodium carbonate, potassium, cesium, lithium,rubidium, or francium based carbonate. In one embodiment, the metal ofthe metal carbonate is a monovalent ion (e.g., an alkali metal). In oneembodiment, the PCC produced may have a crystal geometry including, forexample, spherical vaterite. In one embodiment, the metal of the metalcarbonate is a divalent ion, such as magnesium, strontium, beryllium,barium, or radium. Magnesium carbonate may also be yielded underconditions where magnesium cation is present in the gypsum or in themetal carbonate (e.g. magnesium carbonate, dolomite, etc.).

The process for converting gypsum into precipitated calcium carbonatefurther includes processing the vaterite by at least one method selectedfrom the group consisting of dewatering, drying, ageing, surfacetreating, size reducing, and beneficiating, wherein the processingconverts the vaterite into a calcite or aragonite polymorph. In oneembodiment, seeding a vaterite PCC with ground calcium carbonate (GCC)in water with a pH ranging from 4 to 9, or 5 to 8, or 6 to 7.7 convertsthe vaterite into a calcite polymorph. For this conversion, a GCC seedis provided in 0.1 wt % to 25 wt %, or 0.5 wt % to 15 wt %, or I wt % to10 wt % relative to the vaterite, and the temperature is maintained atless than 35° C. Further, vaterite can be converted to a calcitepolymorph by adding ammonium hydroxide or other bases, such as sodiumhydroxide, potassium hydroxide or calcium hydroxide to a mixture ofvaterite and water, and adjusting the pH to be greater than or equal to10, or greater than or equal to 10.5, or greater than or equal to 11.For this conversion process, the temperature is maintained at atemperature in a range between about 23° C. and about 80° C., betweenabout 25° C. and about 50° C., or between about 30° C. and about 40° C.According to some embodiments, the conversion process temperature may bemaintained for a time period in a range from about 30 minutes to about12 hours. According to some embodiments, substantially all of thevaterite may be converted into calcite. In one embodiment, the additionof 2 to 10%, 4 to 9%, or 6 to 8% of ammonium bicarbonate to vaterite PCCalso aids in conversion to a calcite polymorph. In terms of convertingvaterite into calcite, the vaterite and water mixture may be in the formof a wet cake or a slurry. In contrast, drying of the vateritestabilizes the vaterite polymorph and prevents it from converting tocalcite.

Alternatively, the vaterite may be stabilized by the presence ofammonium sulfate, and/or the presence of iron materials, or the absenceof ammonium bicarbonate and ammonium sulfate. For instance, the vateritemay be stabilized by the presence of ammonium sulfate even when ammoniumbicarbonate is present such that the ammonium bicarbonate to ammoniumsulfate ratio is between [0:100] and [1:15]. In certain embodiments, thevaterite may be stabilized for 1 day, or 1 week, or a month or longer.

According to a third aspect, the present disclosure relates to a processfor converting gypsum into precipitated calcium carbonate involvingproviding a gypsum, and reacting the gypsum with at least one carbonatesource to produce precipitated calcium carbonate in the form ofvaterite, such that i) the pH of the wet vaterite is less than or equalto 8, ii) the vaterite is dried.

Precipitated Calcium Carbonate (PCC)—Morphologies and Properties

In the present disclosure, the crystalline content of a PCC compositionmay be readily determined through visual inspection by use of, forexample, a scanning electron microscope or by x-ray diffraction. Suchdetermination may be based upon the identification of the crystallineform and is well known to those of skill in the art.

The PCC compositions of the present disclosure are characterized by asingle crystal polymorph content of greater than or equal to 30% byweight relative to the total weight of the composition, greater than orequal to 40% by weight, greater than or equal to 60% by weight, greaterthan or equal to about 80% by weight, or greater than or equal to about90% by weight. In some embodiments, the single crystal polymorph isselected from vaterite, calcite and aragonite. Any of the PCCcompositions of the present disclosure in addition to the single crystalcalcite polymorph of greater than or equal to 30% may further oradditionally comprise at least one polymorph selected from the groupconsisting of vaterite, aragonite and amorphous calcium carbonate. Anyof the PCC compositions of the present disclosure in addition to thesingle crystal aragonite polymorph of greater than or equal to 30% mayfurther or additionally comprise at least one polymorph selected fromthe group consisting of calcite, vaterite and amorphous calciumcarbonate.

In some embodiments, the present disclosure provides a stable PCCcomposition or product. As used herein, stable refers to a polymorphcomposition having less than a 1% conversion of any of its polymorphs(i.e. vaterite, calcite, aragonite, and amorphous calcium carbonate)over a period of at least 24 hours, or at least 48 hours or at least 72hours or one week or one month, or less than 0.75%, or less than 0.5%,or less than 0.25%, or less than 0.2%, or less than 0.1% conversion ofany of its polymorphs. For example, a stable PCC composition productwith a 95% calcite polymorph by weight relative to the total weight ofthe PCC composition will maintain 94-96% by weight calcite, or94.5-95.5% by weight calcite within a period of at least 24 hours. Insome embodiments, the stability may vary according to the morphology ofthe PCC.

The PCC compositions may also be characterized by their particle sizedistribution (PSD). As used herein and as generally defined in the art,the median particle size (also called d₅₀) is defined as the size atwhich 50 percent of the particle weight is accounted for by particleshaving a diameter less than or equal to the specified value.

The PCC compositions may have a d₅₀ in a range from about 0.1 micron toabout 30 microns, for example, from about 1 micron to about 28 microns,from about 2 microns to about 14 microns, from about 2 to about 8microns, from about 1 micron to about 4 microns, or from about 0.1micron to about 1.5 microns. The d₅₀ may vary with the morphology of thePCC. For example, calcite PCC may have a d₅₀ in a range from about 1 toabout 28 microns, such as, for example, from about 1 to about 2 microns,from about 1 to about 5 microns, from about 2 to about 4 microns, orfrom about 4 to about 6 microns. Vaterite PCC may have a d₅₀ in a rangefrom about 0.1 microns to about 30 microns, such as, for example, fromabout 0.1 to about 2 microns, from about 1 to about 20 microns, fromabout 1 to about 10 microns, or from about 2 to about 8 microns.Aragonite PCC may have a d₅₀ in a range from about 0.1 microns to about10 microns, such as, for example from about 1 micron to about 8 microns,from about 1.5 to about 6 microns, or from about 2 to about 4 microns.

According to some embodiments, between about 0.1 percent and about 60percent of the PCC particles are less than about 2 microns in diameter.In other embodiments, between about 55 percent and about 99 percent ofthe PCC particles are less than 2 microns in diameter. According to someembodiments, less than about 1 percent of the PCC particles are greaterthan 10 microns in diameter, such as, for example, less than 0.5 percentof the PCC particles are greater than 10 microns in diameter, or lessthan 0.1% of the PCC particles are greater than 10 microns in diameter.

The PCC compositions may be further characterized by their aspect ratio.As used herein, aspect ratio refers to a shape factor and is equal tothe largest dimension (e.g. length) of a particle divided by thesmallest dimension of the particle orthogonal to it (e.g. width). Theaspect ratio of the particles of a PCC composition may be determined byvarious methods. One such method involves first depositing a PCC slurryon a standard SEM stage and coating the slurry with platinum. Images arethen obtained and the particle dimensions are determined, using acomputer based analysis in which it is assumed that the thickness andwidth of the particles are equal. The aspect ratio may then bedetermined by averaging fifty calculations of individual particlelength-to-width aspect ratios. The PCC compositions may have an aspectratio in a range from about 1-20, for example, from about 1-15, fromabout 2-10, or from about 3-5. The aspect ratio may vary with themorphology of the PCC. For example, calcite PCC may have an aspect ratioin a range from about 1-20, such as, for example, from about 1-10, fromabout 2-5, or from about 1-2. Vaterite PCC may have an aspect ratio in arange from about 1-20, or from about 1-10, such as, for example, fromabout 1-8, from about 2-5, or from about 1-3. Aragonite PCC may have anaspect ratio in a range from about 1-20, such as, for example, fromabout 1-15, from about 2-10, or from about 2-5.

The PCC compositions may also be characterized in terms of theircubicity, or the ratio of surface area to particle size (i.e., how closethe material is to a cube, rectangular prism, or rhombohedron). Incertain embodiments of the present disclosure, a lower surface area isadvantageous. Smaller particles typically have much higher surface area,but small particle size is advantageous for many different applications.Thus PCC products with small particle size material and lower than“normal” surface area are particularly advantageous. Rhombic crystalforms are generally preferred in terms of cubicity. The PCC compositionsmay have a cubicity in a range from about 0.03 to 30, or from about 0.03to 50, for example, from about 0.04 to 45, from about 0.5-20, from about1-15, from about 2-10, or from about 3-5. The cubicity may vary with themorphology of the PCC. For example, calcite PCC compositions may have acubicity in a range from about 0.03 to 50, for example, from about 0.04to 25, from about 0.5-20, from about 1-15, from about 2-10, or fromabout 3-5. Vaterite PCC compositions may have a cubicity in a range fromabout 0.03 to 30, or from about 0.03 to 50, for example, from about 0.1to 30, from about 0.5-25, from about 1-15, from about 2-10, or fromabout 3-8. Aragonite PCC compositions may have a cubicity in a rangefrom about 0.03 to 50, for example, from about 0.1 to 30, from about0.5-20, from about 1-15, from about 2-10, or from about 3-8.

According to some embodiments, the cubic nature of the PCC compositionsmay be determined by the “squareness” of the PCC particles. A squarenessmeasurement generally describes the angles formed by the faces of thePCC particle. Squareness, as used herein, can be determined bycalculating the angle between adjacent faces of the PCC, where the facesare substantially planar. Squareness may be measured using SEM images bydetermining the angle formed by the edges of the planar faces of the PCCparticle when viewed from a perspective that is parallel to the facesbeing measured. FIG. 41 shows an exemplary measurement of squareness.According to some embodiments, the PCC compositions may have asquareness in a range from about 70 degrees to about 110 degrees, forexample, from about 75 degrees to about 105 degrees, from about 80degrees to about 100 degrees, or from about 85 to about 95 degrees. Thesquareness may vary with the morphology of the PCC. For example, calcitePCC compositions may have a squareness in a range from about 70 degreesto about 110 degrees, for example, from about 75 degrees to about 105degrees, from about 80 degrees to about 100 degrees, or from about 85 toabout 95 degrees. Vaterite PCC compositions may have a squareness in arange from about 70 degrees to about 110 degrees, or from about 50degrees to about 95 degrees, for example, from about 50 degrees to about105 degrees, from about 60 degrees to about 100 degrees, or from about50 to about 95 degrees. Aragonite compositions may have a squareness ina range from about 1 degrees to about 179 degrees, for example, fromabout 5 degrees to about 150 degrees, from about 15 degrees to about 100degrees, or from about 15 to about 45 degrees.

In the present disclosure, the monodispersity of the product refers tothe uniformity of crystal size and polymorphs. The steepness(d₃₀/d₇₀×100) refers to the particle size distribution bell curve, andis a monodispersity indicator. d_(x) is the equivalent sphericaldiameter relative to which x % by weight of the particles are finer.According to some embodiments, the PCC compositions may have a steepnessin a range from about 30 to about 100, such as, for example, in a rangefrom about 33 to about 100, from about 42 to about 76, from about 44 toabout 75, from about 46 to about 70, from about 50 to about 66, fromabout 59 to about 66, or from about 62 to about 65. According to someembodiments, the PCC compositions may have a steepness in a range fromabout 20 to about 71, such as, for example, in a range from about 25 toabout 50. In some embodiments, the steepness may vary according to themorphology of the PCC. For example, calcite may have a differentsteepness than vaterite.

According to some embodiments, the PCC compositions may have a top-cut(d₉₀) particle size less than about 2 microns to 25 microns, such as,for example, less than about 17 microns, less than about 15 microns,less than about 12 microns, or less than about 10 microns. According tosome embodiments, the PCC compositions may have a top-cut particle sizein a range from about 2 microns to about 25 microns, such as, forexample, in a range from about 15 microns to about 25 microns, fromabout 10 microns to about 20 microns, or from about 3 microns to about15 microns. In some embodiments, the top-cut particle size may varyaccording to the morphology of the PCC. For example, calcite may have adifferent top-cut particle size than vaterite.

According to some embodiments, the PCC compositions may have abottom-cut (d₁₀) particle size less than about 4 microns, such as, forexample, less than about 2 microns, less than about 1 micron, less thanabout 0.7 microns, less than about 0.5 microns, less than 0.3 microns,or less than 0.2 microns. According to some embodiments, the PCCcompositions may have a bottom-cut particle size in a range from about0.1 micron to about 4 microns, such as, for example, in a range fromabout 0.1 micron to about 1 micron, from about 1 micron to about 4microns, or from about 0.5 microns to about 1.5 microns. In someembodiments, the bottom-cut particle size may vary according to themorphology of the PCC. For example, calcite may have a differentbottom-cut particle size than vaterite. For example, vaterite andcalcite may have a bottom-cut particle size in a range from about 0.1micron to about 4 microns and aragonite may have a bottom-cut particlesize in a range from about 0.05 micron to about 4 microns.

The PCC compositions may additionally be characterized by their BETsurface area. As used herein, BET surface area refers to theBrunauer-Emmett-Teller (BET) explaining the physical adsorption of gasmolecules on a solid surface. It refers to multilayer adsorption, andusually adopts non-corrosive gases (i.e. nitrogen, argon, carbon dioxideand the like) as adsorbates to determine the surface area data. The BETsurface area may vary according to the morphology of the PCC. Accordingto some embodiments, the PCC may have a BET surface area less than 80m²/g, such as, for example, less than 75 m²/g, less than 50 m²/g, lessthan 20 m²/g, less than 15 m²/g, less than 10 m²/g, less than 5 m²/g,less than 4 m²/g, or less than 3 m²/g. In some embodiments, the calcitePCC composition particles may have a BET surface area in a range from 1to 30 m²/g, such as, for example, from 2 to 20 m²/g, from 3 to 10 m²/g,from 3 to 5.0 m²/g. In other embodiments, calcite PCC may have a BETsurface area in a range from 1 to 6 m²/g, from 1 to 4 m²/g, from 3 to 6m²/g, or from 1 to 10 m²/g, from 2 to 10 m²/g, or from 5 to 10 m²/g.According to some embodiments, calcite PCC may have a BET surface arealess than or equal to 30 m²/g. Vaterite PCC may have a BET surface areain a range from 5 to 75 m²/g, such as, for example, from 10 to 60 m²/g,from 20-50 m²/g, from 25 to 40 m²/g, or from 30 to 35 m²/g In certainembodiments, the vaterite PCC composition particles have a BET surfacearea in a range from 7 to 18 m²/g, from 5 to 20 m²/g, or from 7 to 15m²/g. Aragonite PCC may have a BET surface area in the range from 2 to30 m²/g, such as, for example, from 5 to 20 m²/g or from 10 to 15 m²/g.

The PCC compositions may additionally be characterized by the ratio ofBET surface area to d₅₀. In a certain embodiment, the vaterite PCCcomposition particles have a ratio of BET surface area to d₅₀ of 1-6.5,2-5.5, or 2.5-5. In another embodiment, the calcite PCC compositionparticles have a ratio of BET surface area to d₅₀ of 0.6-2, 0.7-1.8, or0.8-1.5.

The PCC compositions may additionally be characterized by their stearicacid uptake surface area. As used herein, stearic acid uptake surfacearea refers to a surface treatment of the PCC compositions with stearicacid. Under controlled conditions, the stearic acid may form a monolayeron the surface of the PCC and thus provide information regarding thesurface area via adsorption or uptake of stearic acid. The stearic aciduptake surface area may vary according to the morphology of the PCC.According to some embodiments, the PCC may have a stearic acid uptakesurface area less than 80 m²/g, such as, for example, less than 75 m²/g,less than 50 m²/g, less than 20 m²/g, less than 15 m²/g, less than 10m²/g, less than 5 m²/g, less than 4 m²/g, or less than 3 m²/g. In someembodiments, the calcite PCC composition particles have a stearic aciduptake surface area in a range from 1 to 30 m²/g, such as, for example,from 2 to 20 m²/g, from 3 to 10 m²/g, from 3 to 5.0 m²/g. In otherembodiments, calcite PCC may have a stearic acid uptake surface area ina range from 1 to 6 m²/g, from 1 to 4 m²/g, from 3 to 6 m²/g, or from 1to 10 m²/g, from 2 to 10 m²/g, or from 5 to 10 m²/g. According to someembodiments, calcite PCC may have a stearic acid uptake surface arealess than or equal to 30 m²/g. Vaterite PCC may have a stearic aciduptake surface area in a range from 5 to 75 m²/g, such as, for example,from 10 to 60 m²/g, from 20-50 m²/g, from 25 to 40 m²/g, or from 30 to35 m²/g. In certain embodiments, the vaterite PCC composition particleshave a stearic acid uptake surface area in a range from 7 to 18 m²/g,from 5 to 20 m^(Z)/g, or from 7 to 15 m²/g. Aragonite PCC may have astearic acid uptake surface area in the range from 2 to 30 m²/g, suchas, for example, from 5 to 20 m²/g or from 10 to 15 m²/g.

In some embodiments, the yield of PCC using the process herein isgreater than 50%, greater than 60%, greater than 80%, or greater than90%.

In some embodiments, the PCC compositions comprise substantiallyprecipitated calcium carbonate (CaCO₃). In addition to CaCO₃, variousorganic or inorganic materials may be present in the PCC compositionsincluding, but not limited to, iron (Fe), ammonium hydroxide (NH₄OH),ammonium carbonate (NH₄)₂CO₃, ammonium sulfate (NH₄)₂SO₄, calciumsulfate (CaSO₄), magnesium carbonate (MgCO₃), calcium oxide (CaO) andcombinations thereof. In some embodiments, the PCC compositioncomprising vaterite PCC, calcite PCC, aragonite PCC and/or amorphous PCCand/or mixtures thereof comprise at least one of these impurities. Insome embodiments, the quantity of these impurities present may varyaccording to morphology of the PCC and/or the methods and techniquesused in their formation.

In some embodiments, the PCC composition has a NH₄OH content by weightrelative to the total weight of the PCC composition of less than 35 wt%, such as, for example, less than 30 wt %, less than 25 wt %, less than20 wt %, less than 15 wt %, less than 10 wt %, less than 5 wt % or lessthan 2 wt %. In some embodiments, the PCC composition has a NH₄OHcontent by weight relative to the total weight of the PCC compositionfrom 0 to 35 wt %, from 1 to 30 wt %, from 2 to 25 wt %, from 3 to 20 wt%, from 4 to 15 wt %, or from 5-10 wt %.

In some embodiments, the PCC composition has a (NH₄)₂CO₃ content byweight relative to the total weight of the PCC composition of less than40 wt %, such as, for example, less than 35 wt %, less than 30 wt %,less than 25 wt %, less than 20 wt %, less than 15 wt %, less than 10 wt%, less than 5 wt % or less than 2 wt %. In some embodiments, the PCCcomposition has a (NH₄)₂CO₃ content by weight relative to the totalweight of the PCC composition from 0 to 40 wt %, from 1 to 35 wt %, from2 to 30 wt %, from 3 to 25 wt %, from 4 to 20 wt %, from 5-15 wt %, orfrom 5-10 wt %.

In some embodiments, the PCC composition has a (NH₄)₂SO₄ content byweight relative to the total weight of the PCC composition of less than35 wt %, such as, for example, less than 30 wt %, less than 25 wt %,less than 20 wt %, less than 15 wt %, less than 10 wt %, less than 5 wt% or less than 2 wt %. In some embodiments, the PCC composition has a(NH₄)₂SO₄ content by weight relative to the total weight of the PCCcomposition from 0 to 35 wt %, from 1 to 30 wt %, from 2 to 25 wt %,from 3 to 20 wt %, from 4 to 15 wt %, or from 5 to 10 wt %.

In some embodiments, the PCC composition has a CaSO₄ content by weightrelative to the total weight of the PCC composition of less than 50 wt%, such as, for example, less than 40 wt %, less than 35 wt %, less than30 wt %, less than 25 wt %, less than 20 wt %, less than 15 wt %, orless than 12 wt %. In some embodiments, the PCC composition has a CaSO₄content by weight relative to the total weight of the PCC compositionfrom 10 to 50 wt %, from 15 to 40 wt %, from 20 to 35 wt %, or from 25to 30 wt %.

In some embodiments, the PCC composition has a MgCO₃ content by weightrelative to the total weight of the PCC composition of less than 50 wt%, such as, for example, less than 40 wt %, less than 35 wt %, less than30 wt %, less than 25 wt %, less than 20 wt %, less than 15 wt %, lessthan 10 wt %, or less than 5 wt %. In some embodiments, the PCCcomposition has a MgCO₃ content by weight relative to the total weightof the PCC composition from 2 to 50 wt %, from 5 to 40 wt %, from 10 to35 wt %, from 15 to 30 wt % or from 20 to 25 wt %.

In some embodiments, the PCC composition has a CaO content by weightrelative to the total weight of the PCC composition of less than 10 wt%, such as, for example, less than 9 wt %, less than 8 wt %, less than 7wt %, or less than 6 wt %. In some embodiments, the PCC composition hasa CaO content by weight relative to the total weight of the PCCcomposition from 5 to 10 wt %, from 6 to 9 wt %, from 7 to 8 wt %, orfrom 7.25 to 7.75 wt %.

In some embodiments, the PCC composition has a Fe content by weightrelative to the total weight of the PCC composition of greater than 0.04wt %, such as, for example, greater than 0.05 wt %, greater than 0.10 wt%, greater than 0.25 wt %, greater than 0.5 wt %, greater than 0.75 wt%, greater than 1 wt %, greater than 2 wt %, or greater than 5 wt %. Insome embodiments, the PCC composition has a Fe content by weightrelative to the total weight of the PCC composition from 0.04 to 10 wt%, from 0.05 to 5 wt %, from 0.06 to 1 wt %, from 0.07 to 0.8 wt %, from0.08 to 0.6 wt %, from 0.1 to 0.5 wt %, or from 0.2 to 0.4 wt %.

Producing precipitated calcium carbonate (PCC) by use of calcinednatural calcium carbonated is well-known and widely used in theindustry. Calcining at extremely high temperatures forces the evolutionof carbon dioxide and the formation of calcium oxide from which theprecipitated calcium carbonate is produced upon consecutive exposure towater and carbon dioxide, termed slaking. The energy consumed incalcining natural calcium carbonate and the concomitant production ofcarbon dioxide pollution is among the high economic and environmentalcosts of these traditional methods. In some embodiments, the PCCcompositions of the present disclosure provide PCC compositions whichemit an amount of carbon dioxide during production (i.e. from gypsum)that is less than an amount of carbon dioxide emitted during theproduction of a PCC by calcining and slaking natural calcium carbonate.

Traditional calcining and slaking processes substantially remove alliron oxide impurities from natural calcium carbonate and therefore formfinal calcium carbonate products with relatively low iron oxideimpurites. The processes described herein do not involve calciningnatural calcium carbonate or slaking/carbonation steps, and thus emitless carbon dioxide leading to a lower carbon footprint. Further, as theprocesses described herein do not involve calcining/slaking steps, thePCC compositions thus produced may have a higher iron content in thefinal PCC product. Thus, one aspect of the present disclosure is a lowcarbon footprint PCC composition. Alternatively, the low carbonfootprint PCC compositions may be thought of as “higher” iron PCCcompositions. In some embodiments, the low carbon footprint PCCcompositions of the present disclosure comprise a first iron contentwhich is inversely correlated with the carbon dioxide emissions of theprocess by which the low carbon footprint PCC composition is produced. APCC composition produced by calcining and slaking natural calciumcarbonate will comprise a second iron content. The first iron content isgreater than the second iron content, indicating a PCC compositionhaving a lower carbon footprint.

In some embodiments, the low carbon footprint PCC composition has a Fecontent by weight relative to the total weight of the low carbonfootprint PCC composition of greater than 0.04 wt %, such as, forexample, greater than 0.05 wt %, greater than 0.10 wt %, greater than0.25 wt %, greater than 0.5 wt %, greater than 0.75 wt %, greater than 1wt %, greater than 2 wt %, or greater than 5 wt %. In some embodiments,the low carbon footprint PCC composition has a Fe content by weightrelative to the total weight of the low carbon footprint PCC compositionfrom 0.04 to 10 wt %, from 0.05 to 5 wt %, from 0.06 to 1 wt %, from0.07 to 0.8 wt %, from 0.08 to 0.6 wt %, from 0.1 to 0.5 wt %, or from0.2 to 0.4 wt %. In some embodiments, the Fe content by weight may varyaccording to the morphology of the low carbon footprint PCC and themethods used to produce the low carbon footprint PCC.

The PCC compositions of the present disclosure may be in any desiredform, including but not limited to, powders, crystalline solids, or indispersed form, i.e., the PCC compositions may be dispersed in a liquid,such as in an aqueous medium. In one embodiment, the dispersed PCCcomposition comprises at least about 50% PCC by weight relative to thetotal weight of the dispersion, at least about 70% PCC by weight. Thedispersed PCC composition may comprise at least one dispersing agent,which may be chosen from dispersing agents now known in the art orhereafter discovered for the dispersion of PCC. Examples of suitabledispersing agents include, but are not limited to: polycarboxylatehomopolymers, polycarboxylate copolymers comprising at least one monomerchosen from vinyl and olefinic groups substituted with at least onecarboxylic acid group, and water soluble salts thereof. Example ofsuitable monomers include, but are not limited to, acrylic acid,methacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleicacid, maleic anhydride, isocrotonic acid, undecylenic acid, angelicacid, and hydroxyacrylic acid. The at least one dispersing agent may bepresent in the dispersed PCC composition in an amount ranging from about0.01% to about 2%, from about 0.02% to about 1.5% by weight relative tothe total weight of the dispersion.

FGD gypsum typically contains contaminants and is of low whiteness andbrightness. Major contributors to discoloration may include insolubleimpurities, such as pyrite and various organic species. In the presentdisclosure, gypsum may be pretreated prior to reaction with a carbonatesource. In one embodiment, this pretreatment includes, but is notlimited to, a filtration or sieving step and/or a mineral acid treatmentstep. The filtration method may be, but is not limited to vacuumfiltration.

Fully dissolved gypsum may be filtered or centrifuged to remove theimpurities that result in low whiteness and brightness. The filtrationmethod may be, but is not limited to vacuum filtration, but may refer toany dewatering process common to the art. Furthermore, largecontaminants may be removed from the gypsum by sieving. Alternatively, amineral acid, such as nitric acid, may be employed to improve whitenessand brightness of the gypsum by removing species causing discoloration.A mineral acid may also be employed to remove remaining carbonatespecies in the gypsum. Therefore, in terms of methods A and B whereinmineral acid is added to remove excess carbonate, additional mineralacid may be added to remove non-carbonate contaminants. Additionally,the mineral acid addition step of methods A and B to remove carbonateimpurities may be different from the mineral acid used to removecontaminants resulting in low whiteness and brightness, and the step toremove carbonate impurities may take place prior to the step to removecontaminants resulting in low whiteness and brightness, and vice versa.Thus, it is envisioned within the scope of the present disclosure thatin methods A-I, the method may be modified to include a step forremoving impurities and/or improving the whiteness and brightness of thegypsum by filtering from the fully dissolved gypsum, sieving, and/orutilizing a mineral acid. According to some embodiments, the PCCcompositions may have low ionic impurities. According to someembodiments, the low ionic impurities may improve the electricalproperties of the PCC or a finished product containing the PCC. It isenvisioned that this pretreatment step is performed prior to reactinggypsum with the carbonate source, additive, or seed and that a gypsum ofimproved whiteness and brightness may yield, after reaction with acarbonate source, a PCC product of whiteness and brightness similar tothat of the cleaned gypsum. Polymorph and particle size of the PCCyielded may be controlled using methods disclosed herein, in one or moreof their embodiments.

Brightness refers to a measure of directional reflectance from amaterial of light at a certain wavelength or certain wavelengths. Asused herein, ISO brightness refers to an ISO standard that quantifiesthe brightness of a substantially white or near-white material (i.e.paper) as it would be perceived in an environment that is illuminatedwith a mixture of cool-white fluorescence and some filtered daylight,specifically blue light of specific spectral and geometriccharacteristics, generally ˜457 nm. In some embodiments, the ISObrightness may be determined by a standard test for brightness, such asASTM D985-97. According to some embodiments, the PCC compositions orpaper or paperboard materials comprising them may have an ISO brightnessgreater than or equal to 54, such as, for example, greater than or equalto 65, greater than or equal to 85, greater than or equal to 88, greaterthan or equal to 90, greater than or equal to 92, greater than or equalto 94, or greater than or equal to 95. According to some embodiments,the PCC compositions have a consistent or homogeneous brightness acrossthe PCC particles. According to some embodiments, the PCC compositionsmay have an ISO brightness in the range of about 54 to about 99, suchas, for example, in a range from about 54 to about 97, from about 54 toabout 96, from about 60 to about 95, from about 75 to about 95, fromabout 80 to about 95, or from about 85 to about 90. In some embodiments,the ISO brightness may vary according to the morphology of the PCC. Forexample, calcite may have a different ISO brightness than vaterite.

As used herein, DIN yellowness index refers to an DIN standard thatquantifies and provides numbers that correlate with visual ratings ofyellowness or whiteness of white and near-white or colorlessobject-color samples. In some embodiment, the DIN yellowness index maybe determined by a standard test for yellowness, such as ASTM E313-15e1.According to some embodiments, the PCC compositions or paper orpaperboard materials comprising them may have a DIN yellowness index ofless than or equal to 10.5, such as, for example, less than or equal to8, less than or equal to 5, less than or equal to 2, less than or equalto 1, less than or equal to 0.8, less than or equal to 0.75. Accordingto some embodiments, the PCC compositions have a consistent orhomogeneous DIN yellowness index across the PCC particles. According tosome embodiments, the PCC compositions may have a DIN yellowness indexin the range of about 0.7 to about 10.3, such as, for example, in arange from about 0.8 to about 8, from about 0.9 to about 6, from about1.0 to 3, or from about 1.0 to about 1.5. In some embodiments, the DINyellowness index may vary according to the morphology of the PCC. Forexample, calcite may have a different DIN yellowness index thanvaterite.

Rhombic precipitated calcium carbonate of a particular size distributioncan be yielded from FGD gypsum by reacting with ammonium carbonate inthe presence of a calcium carbonate crystal seed and by controllingreaction parameters as disclosed herein. Rhombic PCC generated from thismethod has similar properties to either rhombic produced by traditionalmethods or ground calcium carbonate (GCC).

Reaction of gypsum with carbonate in the presence or absence ofadditives to yield the rhombic PCC can be carried out in a batch orcontinuous process. Specific selection of reaction conditions aid infine-tuning the properties of the PCC generated. The following may becontrolled for rhombic PCC production disclosed herein: concentration ofgypsum and other reactants, starting temperature for each reactant,reaction temperature and reaction time, drying temperature, annealingtemperature for generated PCC where employed, selection and maintenanceof pH and ionic strength for each solution, addition rate of each addedcomponent, and rate of CO₂ addition, where employed.

PCC may be surface treated with stearic acid, other stearate orhydrocarbon species to yield a specific level of hydrophobicity.Hydrophobicity may be measured using a moisture uptake (MPU) technique,in which a PCC powder is exposed to a high relative humidity atmospherefor 24 h or longer and the weight change due to water sorption isrecorded. In general, the maximum reduction in MPU achievable by surfacetreatment is particularly advantageous. Hydrophobicity may also bemeasured by contact angle, in which a droplet of a test liquid (e.g.water) is placed on a PCC powder and is observed to see whether thedroplet is absorbed (wets) or gives a stable droplet with a measurablecontact angle. Surface treatments may involve dry or wet coating with aC₆-C₂₂ fatty acid or fatty acid salt. Such treatments are well-known inthe art, and in addition to stearic acid, include such materials asammonium stearate, sodium stearate, palmitic acid, and others. The fattyacid/fatty acid salt is provided in sufficient quantity to coat asubstantial portion of the surface of the majority of PCC particles. Theamount of hydrophobizing agent needed to coat a substantial portion ofthe PCC surface is related to the PCC surface area. In one embodiment, acalcite PCC of this disclosure requires 0.5-1.0% hydrophobizing agent tocoat the surface. In another embodiment, a vaterite PCC requires2.0-3.0% hydrophobizing agent to coat the surface. Treated and untreatedPCC or blends thereof, of single or blended size distributions can beused in a variety of applications, including adhesives and sealants as arheology modifier, in paints and ink for opacity and as an extender, asa paper filler, for surface finishing and brightness, a functionalfiller in plastics and as an extender. According to some embodiments,the hydrophobizing agent may form a monolayer on the surface of the PCC.According to some embodiments, the amount of hydrophobizing agent may bein a range from about 0.15 m²/g to about 18 m²/g to coat the particles,such as, for example, in a range from about 0.15 m²/g to about 8 m²/g orfrom about 10 m²/g to about 17 m²/g. The amount of hydrophobizing agentmay be dependent on the morphology of the PCC. For example, calcite PCCmay have an amount of hydrophobizing agent in a range from about 0.15m²/g to about 20 m²/g to coat the particles, and vaterite PCC may havean amount of hydrophobizing agent in a range from about 10 m²/g to about80 m²/g to coat the particles.

In some embodiments, a size reduction method is employed either in situor on the product after recovery. A size reduction method may includesonication or grinding. Since the products appear to exhibit‘substructure’ that is most likely interpretable as aggregation, a sizereduction method may break apart the aggregates into their constituentbuilding blocks. According to some embodiments, ultrasound may be usedto break down agglomerates.

According to some embodiments, the PCC may be beneficiated by grindingor milling. In some embodiments, the beneficiation may include one ormore of magnetic separation, bleaching, or acid washing. The separation,bleaching, or acid washing may occur before the grinding/milling, afterthe grinding/milling, or both.

The PCC compositions of the present disclosure may optionally compriseat least one added pigment. Suitable pigments are those now known orthat may be hereafter discovered. Exemplary pigments include, but arenot limited to, titanium dioxide, calcined clays, delaminated clays,talc, calcium sulfate, other calcium carbonate, kaolin clays, calcinedkaolin, satin white, plastic pigments, aluminum hydrate, and mica.

The pigment may be present in the PCC compositions of the presentdisclosure in an amount less than about 70% by weight relative to thetotal weight of the composition. It is to be understood that the skilledartisan will select any amounts of the optional at least one second PCCform and the optional at least one pigment in such a way so as to obtainvarious desired properties without affecting, or without substantiallyaffecting, the advantageous properties of the PCC compositions disclosedherein.

A Process for Converting Limestone into Precipitated Calcium Carbonate

The present disclosure also relates to a process for convertinglimestone, marble, or chalk into precipitated calcium carbonatecomprising i) treating limestone, marble, or chalk with a mineral acidcomprising sulfate anions to yield a calcium sulfate and magnesiumsulfate mixture ii) optionally adding a calcium carbonate seed to thecalcium sulfate iii) optionally adding an additive to the calciumsulfate iv) reacting the calcium sulfate with at least one carbonatesource selected from the group consisting of ammonium carbonate,ammonium bicarbonate, ammonium carbamate, calcium carbonate, dolomite, ametal carbonate, and carbon dioxide at a reaction temperature of 8-50°C. and a reaction time of 5-250 minutes, to yield precipitated calciumcarbonate and v) isolating the precipitated calcium carbonate. In acertain embodiment, reaction conditions are used to control thecrystalline polymorph and particle size of the precipitated calciumcarbonate thus obtained.

Limestone is a sedimentary rock composed largely of the minerals calciteand aragonite. Dolomitic quicklime is calcined dolomite that isrehydrated (e.g., MgOH and CaOH).

Certain embodiments of the present disclosure relate to a low energymethod of producing precipitated calcium carbonate of controlledpolymorph and particle size with limestone, marble, or chalk as thecalcium source. Treating an impure calcium carbonate source withsulfuric acid generates sulfate products, including calcium sulfate(gypsum) and magnesium sulfate. Then, after treatment with ammoniumcarbonate or a metal carbonate, a PCC and sulfate-based solution-phasebyproduct are generated. The polymorph and particle size of PCCgenerated from gypsum produced in this process can be controlled bymethods disclosed within, in one or more of their embodiments. The useof sulfuric acid and limestone to generate gypsum is known in the art.However, the controlled precipitation of calcium carbonate to generateone or more various PCC polymorphs has not been previously described.Separately, magnesium carbonate can be generated from MgSO₄ formedduring dolomitic limestone reaction with sulfuric acid and dissolved inthe aqueous phase by reaction with an appropriate carbonate.

In one embodiment, the amount of sulfuric acid added to limestone isoptionally a molar equivalent of or in excess of the amount of calciumpresent in the limestone.

Exemplary Precipitated Calcium Carbonate Compounds

The present disclosure relates to a precipitated calcium carbonatecompound with a vaterite polymorph. The vaterite precipitated calciumcarbonate described within has novel structural characteristics, such asparticle size distribution (PSD), steepness, and BET surface area, ascompared to heretofore known vaterite precipitated calcium carbonate.See Table 3 below for vaterite characteristics.

TABLE 3 IMERYS IMERYS Calcite Vaterite PSD (d50), 1.5-28 1.5-28  d30/d70× 100  73.5-59.5 69.0-43.3  Surface Area (BET), m²/g 0.4-20 8-17 SurfaceArea (Stearic Acid uptake), m²/g 0.4-20 8-17

The PCC compositions may also be characterized in terms of theircubicity, or the ratio of surface area to particle size (i.e., how closethe material is to a perfect cube). According to certain embodiments ofthe present disclosure, a lower surface area is advantageous. Smallerparticles typically have much higher surface area, but small particlesize is advantageous for many different applications. Thus PCC productswith small particle size material and lower than “normal” surface areaare particularly advantageous. Rhombic crystal forms are generallypreferred in terms of cubicity.

An example of a qualitative understanding of cubicity can be shown bycomparing FIG. 14 with FIG. 24. FIG. 14 shows a PCC composition having arelatively low surface area to particle size ratio because of therelatively smooth, planar faces of the particles. FIG. 24, by contrast,shows a PCC composition having relatively non-planar faces because ofprotrusions on the faces of the particles, and therefore, thecomposition shown has a higher surface area and a lower cubicity.

FIG. 41 shows an exemplary measurement of squareness. According to someembodiments, the PCC compositions may have a squareness in a range fromabout 70 degrees to about 110 degrees. Five measurements of anglesbetween the planar faces of the PCC particles in FIG. 41 were takenusing IMAGE J analysis software, one of which is shown in FIG. 41.Angles were measured by randomly selecting particles from those havingfaces normal to the plane of the image. The measured angles between theedges were 74.6 degrees, 105.2 degrees, 109.6 degrees, 82.6 degrees, and74.3 degrees. According to some embodiments, the squareness of the PCCparticles may be in a range from about 70 degrees to about 110 degrees,such as, for example, in a range from about 75 degrees to about 105degrees, or from about 80 degrees to about 110 degrees.

In the present disclosure, the monodispersity of the product refers tothe uniformity of crystal size and polymorphs. The steepness(d₃₀/d₇₀×100), as defined above, refers to the particle sizedistribution bell curve, and is a monodispersity indicator. In thepresent disclosure, the preferred PCC product is monodisperse with asteepness greater than 30, or greater than 40, or greater than 50, andless than 60, or even less than 65. According to some embodiments, thePCC may have a steepness in a range from about 30 to about 100, such as,for example, in a range from about 34 to about 100, from about 42 toabout 77. In some embodiments, the steepness may vary according to themorphology of the PCC. For example, calcite may have a differentsteepness than vaterite.

The present disclosure enables the generation of varied PSD (d₅₀) andpolymorphs of the PCC product, which can be formed as vaterite,aragonite, calcite (e.g., rhombic or scalenohedral calcite), oramorphous calcium carbonate. In general, lower reaction temperatureyields smaller/finer, higher surface area vaterite ‘balls’. In general,lower excess of ammonium carbonate yields smaller/finer crystals withinaggregates, and higher surface area products often comprised of acalcite/vaterite blend.

In one embodiment, the PCC composition of the present disclosure ischaracterized by a single vaterite crystal polymorph content of greaterthan or equal to 30% by weight relative to the total weight of thecomposition, greater than or equal to 40% by weight, greater than orequal to 60% by weight, greater than or equal to about 80% by weight, orgreater than or equal to about 90% by weight.

In one embodiment, the vaterite PCC has a geometry comprising sphericalcoral, elliptical coral, rhombic, flower-shaped or mixtures thereof.

In another embodiment, the vaterite PCC has a PSD (d₅₀) ranging from0.1-30, 1-28, 2.0-7.0, 2.4-6.0, or 2.6-5.5 microns.

In another embodiment, the vaterite PCC has a steepness (d₃₀/d₇₀×100)ranging from 30-100, 37-100, 40-83, 42-71.

In another embodiment, the vaterite PCC has a BET surface area rangingfrom 1-75, 5-75, 1-30, 2-30, 8-18, 10-17, or 10.4-16.1 m²/g.

In another embodiment, the vaterite PCC may have an amount ofhydrophobizing agent in a range from about 10 m²/g to about 17 m²/g tocoat the particles.

The present disclosure also relates to a precipitated calcium carbonatecompound with a calcite polymorph. The calcite precipitated calciumcarbonate described within has improved structural characteristics, suchas particle size distribution (PSD), steepness, and BET surface area, ascompared to heretofore known calcite precipitated calcium carbonate. SeeTable 3 for a comparison of calcite manufactured from the process hereinand a known PCC calcite.

In one embodiment, the PCC composition of the present disclosure ischaracterized by a single calcite crystal polymorph content of greaterthan or equal to 30% by weight relative to the total weight of thecomposition, greater than or equal to 40% by weight, greater than orequal to 60% by weight, greater than or equal to about 80% by weight, orgreater than or equal to about 90% by weight.

In one embodiment, the calcite PCC has a rhombic geometry. In general,seeding gypsum with crystallized calcium carbonate consistently yieldsrhombic PCC. Seeding with calcite, dolomite, or magnesite yields rhombicPCC. In general, seeding with coarse scalenohedral PCC>5% yields alarger/coarser and a higher surface area product. In general, seedingwith fine rhombohedral PCC<5% yields a finer crystal size within theaggregate; >5% gives finer aggregates. In the absence of seeding,ammonium carbonate conditions influence rhombic PCC formation.

In one embodiment, rhombic PCC yielded may be small stacked plates of300-500 nm, forming inconsistent or consistent particle shapes, having ado of 1-28 μm or 1-6 μm, a steepness of 30-100 or 56-91, and a BETsurface area of 1-30 m²/g or 2-5 m²/g.

Table 4 below identifies product characteristics obtained from variousexamples of the foregoing methods.

TABLE 4 Particle Size Distribu- Individual tion (d50), Steepness SurfaceParticle agglomerates (d30/d70 × Area PCC SEM Size (est.) (μm) 100)(m²/g) Rhom- See 300-500 nm 4.6 60 4.6 bic FIG. 8 Rhom- See 1-2 μm 4.961 2.6 bic FIG. 9 Rhom- See ~5 μm 27.1 73 2.8 bic FIG. 10

In another embodiment, the calcite PCC has a PSD (d₅₀) ranging from1-28, 1.8-6.0, 2.2-5.8, or 2.8-5.6 microns.

In another embodiment, the calcite PCC has a steepness (d₃₀/d₇₀×100)ranging from 30-100, 40-100, 50-83, 56-71.

In another embodiment, the calcite PCC has a BET surface area rangingfrom 2-25, 3.0-7.0, 3.1-6.0, or 3.5-5.0 m²/g.

In another embodiment, the calcite PCC may have an amount ofhydrophobizing agent in a range from about 0.15 m²/g to about 8 m²/g tocoat the particles.

The present disclosure also relates to a precipitated calcium carbonatecompound with an aragonite polymorph. The aragonite precipitated calciumcarbonate described within has improved structural characteristics, suchas particle size distribution (PSD), steepness, and BET surface area, ascompared to heretofore known aragonite precipitated calcium carbonate.

In one embodiment, the PCC compound of the present disclosure ischaracterized by a single aragonite crystal polymorph content of greaterthan or equal to 30% by weight relative to the total weight of thecomposition, greater than or equal to 40% by weight, greater than orequal to 60% by weight, greater than or equal to about 80% by weight, orgreater than or equal to about 90% by weight.

According to some embodiments, after forming the PCC compound of thepresent disclosure, the morphology may be changed throughpost-processing techniques, such as aging. For example, according tosome embodiments, an amorphous PCC may be used as a precursor to convertinto a crystalline morphology, such as vaterite, aragonite, or calcite.According to some embodiments, a metastable PCC, such as vaterite oraragonite, may be converted to calcite through aging, such as, forexample, wet aging. The amount of vaterite converted to calcite throughaging may be varied by adjusting the properties of the aging conditions.For example, the aging may be varied by the presence or absence ofammonium sulfate, including the amount of ammonium sulfate, the agingtemperature, and the concentration of wet cake solids. According to someembodiments, when less than about 90% vaterite is present, the vateritewill convert to calcite. When greater than or equal to about 90%vaterite is present, the vaterite can be retained in a dry powder or wetcake. The amount of retained vaterite may vary depending on the agingparameters. According to some embodiments, vaterite can be converted tocalcite through a mechanical process, such as by grinding or ballmilling the vaterite.

According to some embodiments, the concentrations of gypsum and ammoniumcarbonate may influence the conversion of vaterite to calcite. Forexample, higher concentrations of gypsum and ammonium carbonate mayproduce vaterite PCC that is more stable (e.g., resistant to convertingto calcite) than vaterite PCC produced using lower concentrations ofgypsum and ammonium carbonate. For example, when 10.7% gypsum and 12.5%ammonium carbonate (1:1.7 molar ratio [gypsum:ammonium carbonate]) arereacted at room temperature, the reaction forms vaterite that convertsto calcite in the presence of ammonium sulfate within 24 hours. Whenhigher concentrations of gypsum and ammonium carbonate are used in thereaction, the vaterite produced may be more stable. For example, when35% gypsum and 33% ammonium carbonate (1:1.7 molar ratio[gypsum:ammonium carbonate]) are reacted at room temperature, thereaction forms vaterite, but the vaterite is stable in the presence ofammonium sulfate for at least 24 hours. In other embodiments,impurities, such as, for example, iron present in either gypsum orammonium-based carbonates may assist stabilizing vaterite PCC producedby the methods described herein. According to some embodiments, theconversion of vaterite to calcite may be controlled through the storageof the vaterite. For example, vaterite in liquid suspension withammonium sulfate may convert to calcite may be inhibited relative tocakes of vaterite having about 40-60% solids without ammonium sulfate.According to some embodiments, the conversion of vaterite to calcite mayreduce the surface area of the PCC formed. For example, the conversionof vaterite to calcite may reduce the surface area of the PCC fromgreater than 10 m²/g (vaterite) to less than 1 m²/g (calcite). Accordingto some embodiments, the conversion of vaterite to calcite may increasethe particle size of the PCC. In other embodiments, the conversion ofvaterite to calcite may not significantly change the particle size ofthe PCC. Other additives, such as, for example, citric acid may inhibitthe conversion of vaterite to calcite. For example, about 5% by weightcitric acid on vaterite may inhibit the conversion to calcite. Accordingto some embodiments, adding ammonium bicarbonate may accelerate theconversion of vaterite to calcite, whereas ammonium sulfate inconcentrations from about 0.5% to about 10% by weight may slow orinhibit the conversion to calcite. FIG. 39 shows exemplary effects onmorphology of the PCC by varying the feed concentrations and the agingprocess. FIG. 40 shows exemplary effects of the feed composition on PCC.

According to some embodiments, the methods of forming the PCC compoundmay be performed in a continuous process, such as, for example, using atubular reactor. In some embodiments, in the continuous process, thereactants may be mixed in such a way as to cause cavitation.

Commercial Applications

According to certain embodiments, the present disclosure relates tocommercial applications of the vaterite, calcite, and/or aragoniteprecipitated calcium carbonate compound described herein, in one or moreof its embodiments.

According to a first aspect, the present disclosure relates to a polymerfilm or a breathable polymer film containing the vaterite, calcite,and/or aragonite precipitated calcium carbonate compound in one or moreof its embodiments.

According to a second aspect, the present disclosure relates to a pulpor paper material or product containing the vaterite, calcite, and/oraragonite precipitated calcium carbonate compound in one or more of itsembodiments. In some embodiments, the paper product comprises theprecipitated calcium carbonate as a filler or as a coating. In someembodiments, the paper material or paper product may be a paper towel,an absorbent cloth or a sanitary napkin.

According to a third aspect, the present disclosure relates to a diapercomprising a breathable polymer film containing the vaterite, calcite,and/or aragonite precipitated calcium carbonate compound in one or moreof its embodiments.

According to a fourth aspect, the present disclosure relates to a filledpolymer composition comprising the PCC of the present disclosure in oneor more of its embodiments as filler, wherein the polymer can be anydesired polymer or resin. In some embodiments, the polymeric material ofthe filled polymer composition may be natural or synthetic. In someembodiments, the polymeric material of the filled polymer compositionmay be biodegradable.

According to some embodiments, the PCC compositions may be used as afiller for various applications. Exemplary applications include, but arenot limited to, fillers or additives for plastics, paper coatings,adhesives, sealants, caulks, paper, moldings, coatings, paint, rubberproducts, and concrete. For example, the PCC compositions may be used asa filler or additive for polyvinylchloride (PVC), plasticized PVC(pPVC), polypropylene (PP), rubber, coatings, paint, ceramics, paper, orconcrete. Some exemplary uses include use as a filler or additive forPVC pipes or moldings, pPVC, paint (e.g., exterior paint or road paint),tile coatings (e.g., ceiling tile coatings), decorative coatings,moldings (e.g., PVC moldings, pPVC moldings, or PP moldings), sheetmolding compounds, bulk molding compounds, adhesives, caulks, sealants,rubber products, paper, paper fillers, paper coatings, or concrete.According to some embodiments, the relatively lower surface area of thePCC compositions may be suitable as a filler and may have improveddispersibility. The PCC compositions may, in general, have relativelylow brightness (e.g. 65 ISO brightness) to relatively high brightness(e.g., greater than 90 ISO brightness) and may have a consistentbrightness, which may improve the color of a given product in anapplication. The PCC compositions disclosed herein may have a relativelylow surface area when compared to other calcium carbonate products, suchas, for example, ground calcium carbonate (GCC). The relatively lowsurface area may contribute to low adsorption of additives by the PCC,reduced amounts of additives to treat a surface of the PCC, and/or lowmoisture pick-up by the PCC. According to some embodiments, therelatively lower surface area may contribute to a relatively lowerviscosity of the material to which the PCC is added and/or a greateramount of “active” particles when used as a filler or additive, such as,for example, in polymer films. According to some embodiments, a broadparticle size distribution of the PCC may increase particle packing,whereas a steep or narrow particle size distribution of the PCC maydecrease particle packing. According to some embodiments, a relativelysmaller PCC particle size may improve the gloss of a coating, such as,for example, a paper coating or paint, containing the PCC composition. Arelatively smaller particle size may also improve the impact resistanceof a material, such as, for example, a molded product or coating,containing the PCC composition.

According to some embodiments, the steepness and/or cubicity of the PCCparticles described herein may improve the handling properties ofpowders. For example, the steepness and/or cubicity of the PCC particlesmay improve the flowability of powders.

According to some embodiments, the PCC compositions described herein mayhave improved oil absorption properties. Improved oil absorption may,for example, improve the flowability of paints or powders incorporatingthe PCC compositions.

According to some embodiments, the PCC compositions, such as thevaterite PCC compositions, may further comprise at least one activeingredient, encapsulated, absorbed, adsorbed, or embedded onto or intothe polymorph of the PCC compositions for delivering said activeingredient to a delivery site. In some embodiments, the PCC compositionsmay provide a useful mechanism for delivering active ingredients, suchas synthetic or natural nutritional or health products intact to wherethey are most effective. In some embodiments, the at least one activeingredient is homogeneously distributed throughout the PCC compositions.In some embodiments the at least one active ingredient isheterogeneously distributed throughout the PCC compositions (i.e.concentrated near the surface of the PCC compositions).

According to some embodiments, the PCC compositions, such as thevaterite PCC compositions, may be used for various applications,including but not limited to drug delivery, medical devices, biosensing,encapsulation, tracing, polymer fillers, cavitation enhancement infilms, heavy metal sequestration, as a nucleation agent (for example, afoam nucleation agent), an abrasive, FGD feeds, synthetic papercomponent, or emulsion systems filler. In some embodiments, the PCC,such as calcite or aragonite PCC, may be used as a drug delivery agentor component. For example, vaterite may be used as a platform for smallmolecule or protein absorption or adsorption, such as into the pores ofthe vaterite. Vaterite may also be used, in some embodiments, as amicroparticle or microcapsule for drug encapsulation or drug delivery,for example, vaterite may be used to encapsulate molecules including,but not limited to, insulin, bovine serum albumin, and lysozymes. Insome embodiments, encapsulation may occur during a phase transition ofthe PCC from vaterite to calcite. Such encapsulation may promotecontrolled release of the encapsulated molecules. In some embodiments,encapsulation may occur through absorption or adsorption of themolecules into the pores of the vaterite. In other embodiments,encapsulation may occur through direct encapsulation during theformation of the PCC particles. In other embodiments, encapsulation mayoccur through hollow-centered PCC particles.

According to some embodiments, the PCC, such as calcite or aragonite maybe used as a controlled release agent. For example, vaterite may beexposed to highly acidic environments to control release. Vateriteexposed to such environments may break down, thereby releasing theencapsulant or encapsulated, absorbed, or adsorbed molecules. Accordingto some embodiments, the vaterite may serve as a template proteinstructure to control release of a molecule. According to someembodiments, the vaterite may be used as a template for cross-linkingpolymer, such as, for example, biopolymers. In some embodiments, thepolymers may be cross-linked using the vaterite as a template.Subsequent removal of the vaterite may result in a cross-linked polymerhaving a structure similar to the vaterite template (e.g., spherical).

According to some embodiments, the PCC, such as calcite or aragonite,may be used in medical devices, such as, for example, implantablemedical devices. In some embodiments, vaterite may exhibit rapidbioabsorption, for example, due to vaterite's high surface area. Becauseof rapid absorption, vaterite may be used as a calcium source forbiological applications, such as, for example, bone regeneration.Vaterite may also assist in the generation of bone minerals, such asphosphate bone minerals, such as hydroxyapatite. In some embodiments,the hydroxyapatite or other small molecules may be encapsulated by thevaterite or PCC, or may be bound (either chemically or physically) tothe surface of the vaterite. Conversion of the vaterite to calcite, insome embodiments, may also promote binding of the PCC to bone.

According to some embodiments, the PCC, such as calcite or aragonite,may be used in biosensing applications. For example, vaterite may beused in biosensing of pH changes or ion sensing. In some embodiments, afluorescent pH sensor may be encapsulated by the vaterite, such as, forexample, in tracing applications.

According to some embodiments, the PCC, such as calcite or aragonite maybe used as a filler for polymers. For example, the vaterite may be usedin polymer films, such as, for example, cavitation enhancement. In someembodiments, the vaterite may promote more uniform cavitation of poresand may increase the breathability of the film.

According to some embodiments, PCC, such as calcite or aragonite, mayencapsulate metals, such as heavy metals. For example, encapsulation mayoccur through a phase change from vaterite to calcite.

According to some embodiments, the PCC, such as calcite or aragonite,may be used as a nucleating agent. In some embodiments, the vaterite mayact as a foam nucleating agent.

According to some embodiments, the PCC, such as calcite or aragonite,may be used as an abrasive, such as, for example, a cleaning abrasive.

According to some embodiments, the PCC, such as calcite or aragonite maybe used as a feed material in an FGD process. In some embodiments, theincreased surface area of the vaterite may improve reactivity and/orincrease the reaction rate. For example, the vaterite may neutralizesulfuric acid generated in the FGD process.

According to some embodiments, the properties of the PCC compositions,such as c described in this disclosure may be beneficial for variousapplications. For example, a polymorph shift may be induced under shearand/or heat. For example, the vaterite may convert to needle-likeparticles or rhombic particles. A polymorph shift may, in someembodiments, be influenced by the presence of surfactants ormacromolecules. A polymorph shift may also be influenced by inclusionsin the vaterite structure, such as metals or other ions. For example,polymorph changes may be mitigated through the use of surfactants,reacting the vaterite in the presence of metals, or through the use ofadditives. Additives may include, but are not limited to, acids oradditives for biomineralization, such as, for example, ovalbumin,glutamic acid, or aspartic acid.

The examples below are intended to further illustrate examples of aprocess for desulfurizing flue gas to form gypsum and for convertinggypsum thus obtained or limestone into precipitated calcium carbonatewith desired polymorph and crystal size.

Example 1

Gypsum or other sulfate was slurried in water at 35% solids or in asolution of 30-35% ammonium sulfate. Ammonium carbonate was dissolved inwater at elevated temperature in a concentration to give a 1:1.7[gypsum: ammonium carbonate] molar ratio for reaction. Alternativecarbonate feeds were dissolved in water at room temperature in an amountto give a 1:1.7 [sulfate: carbonate] molar ratio for reaction. Thesulfate slurry and carbonate solution were mixed and allowed to reactfor at least 10 minutes. The slurry was then filtered and the slurrycake washed with water. Reaction cake and decanted liquid werechemically and physically analyzed by FTIR, DSC, SEM, Sedigraph, and BETsurface area analysis. Reactions involving this process are described inTable 1 and 2.

Example 2

For reactions involving ammonium carbonate production from ammoniumhydroxide and CO₂, sulfate was slurried at ambient temperature andpressure as described above. Ammonium hydroxide was added to the sulfateslurry just prior to the mixture being poured in a reaction vessel. Thereaction vessel was covered, then heated or cooled to a selectedtemperature with stirring. CO₂ was bubbled through the reaction vesselwith stirring for a minimum 1 hour. After 1 hour of reaction time, asmall portion of the slurry was removed and checked for full conversionto PCC by phenolphthalein color change. Upon reaction completion, theslurry was removed from the reaction vessel, filtered, washed andanalyzed as described above. Reactions involving this process aredescribed in Table 1.

Exemplary Core Materials with Precipitated Calcium Carbonate

According to some embodiments, one or more of the methods disclosed inthis disclosure may be used to precipitate PCC onto a core material. Forexample, the PCC may form a surface layer or coating that impartsbeneficial properties to the core material. The process may, in someembodiments, be used to precipitate a core material from solution wherethe precipitated core material has a PCC layer or coating. It isunderstood that the use of the word “layer” or “coating” includes aprecipitated calcium carbonate phase formed on at least a portion of thesurface of the core material. In some embodiments, the PCC layer orcoating may cover half or substantially all of the surface of the corematerial. The core material may form the core of a calciumcarbonate-coated composition.

According to some embodiments, the core material may include a weightingagent for use in drilling fluids. The weighting agent may include ironoxide, such as, for example hematite (Fe₂O₃). Other weighting agents maybe used, however, such as, for example, AgI, AgCl, AgBr, AgCuS, AgS,Ag₂S, Al₂O₃, AsSb, AuTe₂, BaCO₃, BaSO₄, BaCrO₄, BaO, BeO, BiOCl,(BiO)₂CO₃, BiO₃, Bi₂S₃, Bi₂O₃, CaO, CaF₂, CaWO₄, CaCO₃, (Ca,Mg)CO₃, CdS,CdTe, Ce₂O₃, CoAsS, Cr₂O₃, CuO, Cu₂O, CuS, Cu₂S, CuS₂, Cu₉S₅, CuFeS₂,CusFeS₄, CuS.Co₂S₃, Fe²⁺Al₂O₄, Fe₂SiO₄, FeWO₄, FeAs₂, FeAsS, FeS, FeS₂,FeCO₃, Fe₂O₃, α-Fe₂O₃, α-FeO(OH), Fe₃O₃, FeTiO₃, HgS, Hg₂Cl₂, MgO,MnCO₃, Mn₂S, MnWO₄, MnO, MnO₂, Mn₂O₃, Mn₃O₃, Mn₂O₇, MnO(OH), CaMoO₄,MoS₂, MOO₂, MOO₃, NbO₄, NiO, NiAs₂, NiAs, NiAsS, NiS, PbTe, PbSO₄,PbCrO₄, PbWO₄, PbCO₃, (PbCl)₂CO₃, Pb²⁺ ₂Pb⁴⁺O₄, Sb₂SnO₅, Sc₂O₃, SnO,SnO₂, SrO, SrCO₃, SrSO₄, TiO₂, UO₂, V₂O₃, VO₂, V₂O₅, VaO, Y₂O₃, YPO₄,ZnCO₃, ZnO, ZnFe₂O₄, ZnAl₂O₄, ZnS, ZrSiO₄, ZrO₂, ZrSiO₄, of combinationsthereof. According to some embodiments, the core material may includetwo or more homogeneous domains, such as, for example, (Ba,Sr)SO₄,(Ba,Sr)CO₃, or Ba(SO₄,CrO₃). In some embodiments, barium sulfate may beused as a weighting agent onto which calcium carbonate is precipitated.

Precipitation of calcium carbonate onto a weighting agent may impartbeneficial properties to the weighting agent. For example, weightingagents, such as iron oxide and barium sulfate, are denser than calciumcarbonate and, therefore, provide a desirable densifying agent whenadded to fluids, such as drilling fluids. These weighting agents, ontheir own, also have a high hardness, which makes them abrasive tomachinery and formations in the earth. As a result, the weighting agentsmay cause abrasion or corrosion of the machinery during us. Byprecipitating calcium carbonate onto the iron oxide or other weightingagent, the relatively lower hardness of the calcium carbonate layer(e.g., about 3 Mohs for calcium carbonate versus about 5.5 Mohs forhematite) reduces the abrasivity of the weighting agent, which mayreduce the abrasion caused during use of the agent.

According to some embodiments, the amount of the calcium carbonatecoating may be tailored to provide a desired specific gravity of theresulting agent. For example, a PCC-coated hematite weighting agent mayhave an amount of PCC to provide a specific gravity of the PCC-coatedhematite that is between the specific gravity of the calcium carbonateand the core material. The modification of the specific gravity of theweighting agent may allow for tailoring the weighting agent to specificapplications.

The choice of weighting agent may also be determined based on theintended application. For example, calcium carbonate and iron oxide aredissolvable in dilute acids, such as, for example, dilute hydrochloricacid (HCl). Choosing a weighting agent and coating with similardissolution properties may permit removal of both the weighting agentand the coating to increase the flow of hydrocarbon by “shocking” thewell with dilute acid to remove the weighting agent.

The precipitation of calcium carbonate onto various core materials alsoallows for a wider distribution of particle sizes in the weightingagent. The particle size distribution may be controlled either by thesize of the weighting agent or the amount of PCC used to coat theparticles.

According to some embodiments, a method of precipitating calciumcarbonate may include providing a core material in solution, addingcalcium sulfate to the solution, adding a carbonate source to thesolution, and precipitating calcium carbonate onto the core material.According to some embodiments, the carbonate source may include ammoniumcarbonate.

According to some embodiments, the precipitated calcium carbonate mayinclude a carbonate material containing calcium and at least one othermetal. For example, the precipitated calcium carbonate may includedolomite (CaMg(CO₃)₂).

According to some embodiments, the core material may be dissolvable indilute acid, such as, for example, hydrochloric acid (HCl).

According to some embodiments, the core material may include a weightingagent. According to some embodiments, the core material may include ironoxide, such as, for example hematite. According to some embodiments, thecore material may include barium sulfate.

According to some embodiments, the precipitated calcium carbonate may bebetween about 10% and about 25% by weight of the combined calciumcarbonate and core material, such as, for example, between about 10% andabout 15% by weight, between about 15% and about 20% by weight, betweenabout 20% and about 25% by weight, between about 12% by weight and about18% by weight, or between about 18% by weight and about 23% by weight ofthe combined calcium carbonate and core material.

According to some embodiments, the precipitated calcium carbonate-corecomposition may have a specific gravity in a range having a lower limitof about 2.6, 3, 4, 4.5, 5, or 5.5 to an upper limit of about 20, 15,10, 9, 8, or 7, and permutations thereof.

According to some embodiments, the precipitated calcium carbonate-corecomposition may be suitable for use in a drilling application. Forexample, the precipitated calcium carbonate-core composition may besuitable for use as a weighting agent in a drilling fluid, such as anadditive to a drilling mud.

Example 3

An exemplary calcium carbonate coated hematite was prepared by reactingcalcium sulfate with ammonium carbonate solution. First, 6.30 grams ofcalcium sulfate from Sigma Aldrich were mixed with 250 mL of water at25° C. for 30 minutes for form a slurry. Next, 20 grams of the Hematitewere added to the slurry and mixed to keep the specific ratio of 84.5%to 15.5% hematite to PCC by weight. Then 5.97 grams of ammoniumcarbonate were dissolved in 250 mL of water and immediately added to theslurry. The final mixture was mixed for 1 hr to precipitate the PCC ontothe hematite. After mixing, the mixture was filtered and washed toremove excess ammonium sulfate. The resulting cake containing thePCC-coated hematite was recovered.

Nothing in the above description is meant to limit the scope of theclaims to any specific composition or structure of components. Manysubstitutions, additions, or modifications are contemplated within thescope of the present disclosure and will be apparent to those skilled inthe art. The embodiments described herein were presented by way ofexample only and should not be used to limit the scope of the claims.

1. A precipitated calcium carbonate having a calcite polymorph thatmeets at least one of the following: a stearic acid uptake surface arearanging from 1 to 30 m²/g; or at least one impurity by weight relativeto the total weight of the precipitated calcium carbonate selected fromthe group consisting of: Fe greater than 0.04 wt %, NH₄OH ranging from 0to 35 wt %, (NH₄)₂CO₃ ranging from 0 to 40 wt %, (NH₄)₂SO₄ ranging from0 to 35 wt %, CaSO₄ ranging from 10 to 50 wt %, MgCO₃ ranging from 2 to50 wt %, and CaO ranging from 5 to 0 wt %.
 2. The precipitated calciumcarbonate having a calcite polymorph of claim 1, which also has a BETsurface area ranging from 1 to 30 m²/g.
 3. The precipitated calciumcarbonate having a calcite polymorph of claim 1, which also has a d₅₀particle size ranging from 1 to 28 μm.
 4. The precipitated calciumcarbonate having a calcite polymorph of claim 1, which also has a d₉₀particle size ranging from 2 to 25 μm.
 5. The precipitated calciumcarbonate having a calcite polymorph of claim 1, which also has a d₁₀particle size ranging from 0.1 to 4 μm.
 6. The precipitated calciumcarbonate having a calcite polymorph of claim 1, which also has asteepness (100×d₃₀/d₇₀) ranging from 30 to
 100. 7. The precipitatedcalcium carbonate having a calcite polymorph of claim 1, which also hasan ISO brightness ranging from 54-96.
 8. The precipitated calciumcarbonate having a calcite polymorph of claim 1, which also has a DINyellow index ranging from 0.7 to 10.3.
 9. A precipitated calciumcarbonate having a calcite polymorph, which emits an amount of carbondioxide during production that is less than an amount of carbon dioxideemitted during the production of a precipitated calcium carbonate havinga calcite polymorph produced by calcining and slaking natural calciumcarbonate.
 10. The precipitated calcium carbonate having a calcitepolymorph of claim 9, which also has a BET surface area ranging from 1to 30 m²/g.
 11. The precipitated calcium carbonate having a calcitepolymorph of claim 9, which also has a stearic acid uptake surface arearanging from 1 to 30 m²/g.
 12. The precipitated calcium carbonate havinga calcite polymorph of claim 9, which also has a d₅₀ particle sizeranging from 1 to 28 μm.
 13. The precipitated calcium carbonate having acalcite polymorph of claim 9, which also has a d₉₀ particle size rangingfrom 2 to 25 μm.
 14. The precipitated calcium carbonate having a calcitepolymorph of claim 9, which also has a d₁₀ particle size ranging from0.1 to 4 μm.
 15. The precipitated calcium carbonate having a calcitepolymorph of claim 9, which also has a steepness (100×d₃₀/d₇₀) rangingfrom 30 to
 100. 16. The precipitated calcium carbonate having a calcitepolymorph of claim 9, which also has an ISO brightness ranging from 54to
 96. 17. The precipitated calcium carbonate having a calcite polymorphof claim 9, which also has a DIN yellow index ranging from 0.7 to 10.3.18. A precipitated calcium carbonate having a low carbon footprint,comprising; a calcite calcium carbonate polymorph, and a first amount ofFe, wherein the first amount of Fe is inversely correlated to carbondioxide emissions, and wherein the first amount of Fe is greater than asecond amount of Fe present in a precipitated calcium carbonate producedby calcining and slaking natural calcium carbonate. 19-27. (canceled)28. A paper product, comprising the precipitated calcium carbonatehaving a calcite polymorph of claim 1, wherein the precipitated calciumcarbonate is present in the paper product as a filler or as a coating.29. The paper product of claim 28, which is a paper towel, an absorbentcloth, or a sanitary napkin.
 30. A polymer comprising a polymericmaterial and a filler, wherein the filler comprises the precipitatedcalcium carbonate having a calcite polymorph of claim
 1. 31-61.(canceled)